Floodlighting
Floodlighting
This module deals with lighting objectives and criteria, equipment, lighting calculations, maintenance and
specific applications for floodlighting. The techniques of floodlighting are applied to both interior and
exterior installations. Roadlighting and amenity lighting are subjects that are not included in this module.
1
Lighting Objectives and Criteria
Objectives
Lighting objectives can include needs such as to:
• allow safe movement of pedestrians, bikes, cars, and
trucks on sites
• attract tourists
• allow the extended use of sports facilities
• deter thieves or vandals.
Associated with these and other objectives are different
lighting design criteria, and also different lighting techniques
to satisfy them. There are some common threads in lighting
design, not least the available equipment and the
design calculations.
The three broad lighting design objectives of safety,
performance, and appearance apply to floodlighting.
Safety and security are the prime concern of the majority of
Fig 1 Emmanual College, Cambridge
installations out of doors, for example the detection of
obstructions by pedestrians or the detection of an intruder by
a guard. Industrial floodlighting is installed in order that visual tasks can be carried out after dark, and so is
sports lighting. Most building floodlighting schemes have a commercial purpose, including tourism, and
some are just for fun, but the important design objective is to provide an enhanced appearance. However,
in translating these objectives into lighting criteria there are two departures from the interior lighting
situation. Firstly, since the visual size of the details to be seen are generally much larger (except
certain sports activities), lower levels of lighting tend to be sufficient. Secondly, whereas most of the visual
details lie on a horizontal plane indoors, the lighting of vertical surfaces tends to be more important
outdoors. Unlike interior lighting, lighting levels are often recommended in broad ranges.
Criteria
Illuminance and uniformity
Fig 2 shows the ranges of average illuminance regarded as satisfactory for various area floodlighting
applications, together with the plane on which it is recommended that this illuminance should be
provided. In many installations where an area is lit there should be limits on the diversity of
illumination provided. For various applications Fig 3 suggests limiting values for two alternative measures
of overall uniformity - the ratio of maximum to minimum illuminance over the critical plane and the
average to minimum ratio - and also the "gradient" or maximum rate of change of illuminance
with distance.
It is obviously necessary to limit the number of points for which the illuminance is calculated in order to
predict the average illuminance and its uniformity. Fig 4 suggests upper and lower limits for the number of
points which provides a satisfactory compromise between accuracy and excessive effort for rectangular
areas of different size. A number of points which is a multiple of two numbers (preferably odd) should be
selected, the points corresponding to the corners of small grid squares making up the rectangular area
(Fig 5). If data is needed on the illuminance gradient at the boundaries, the calculation grid should be
extended to include the points on the dotted lines in Fig 5. These points should not be included in
the calculation of the average value of illuminance for the area. A single value at each grid point suffices
1
Floodlighting
Illuminance range (lux)
1-10
10-50
50-100
Critical plane
Horizontal
Vertical
Horizontal
Horizontal
Vertical
Horizontal
Vertical
Vertical
Vertical
100-500
500-1000
1000-2000
Application
Amenity, general storage areas
Security, causal sports training
Stock and cargo handling, non-critical working areas
car parks (high risk 50 lux)
Critical work areas, sports practice, playgrounds
Aircraft service areas, advertising - unlit roads
Club and tournament sports, sales areas
Advertising - lit roads, spectator sports
Spectator sports
Televised sports events
Fig 2 Illuminance range recommended for exterior lighting
Application
Variation of illuminance in critical plane of
measurement
Uniformity
Diversity
min/average
min/max
Non-critical areas:
parks, gardens,
amenity lighting,
outdoor car parks
Working areas,
sports training areas
Filming and television
Gradient
Minimum distance over which
20% change in illuminance
occurs (m)
0.3
0.5
0.4 (Ev)
0.5 (Eh)
4
Fig 3 Illuminance variation recommended for exterior lighting
Number of grid points
140
120
100
80
60
40
2000
6000
10000
14000
18000
Area (m2)
Fig 4 Number of grid points for an area
Fig 5 Grid for illuminance and uniformity
calculations
when horizontal illuminance is being considered, but this is not so for vertical illuminance. It is then usual
to evaluate the illuminance on each of the four vertical sides of a cube placed at each grid point. The value
of average illuminance and variation on the same faces of the cubes are considered separately. Calculations
of this complexity are usually carried out using a computer.
2
Floodlighting
Direction of lighting & modelling
In an exterior scene it is the highlights and shadows that gives "life"
and achieve modelling, these are created by the direction (a function
of the geometry of the installation) and the intensity of the light. The
impressions of a lit area are subjective and cannot be measured.
Designers mainly rely on experience, supplemented if necessary by
scale model and site experiments, to achieve the desired results.
Photographs of the site during the day can help the design
process. Computer visual simulations in the hands of an experience
designer can help in 'selling' the implementation of the project to the
client by giving an impression of the floodlit scene.
A dramatic effect can be achieved with building floodlighting
by directing the floodlights at a glancing angle to produce strong
shadows and marked highlights. (Fig 6) The shadows can then be
illuminated by light of a contrasting, (usually cooler) colour from the
opposite direction. The shadows on a surface lit by tungsten halogen
or high pressure sodium lamps could be emphasised by using the light
from mercury or metal halide lamps at a lower luminance. Care must
be taken to maintain a coherent light and shade pattern across the
field of view. The designer must consider the visual impact and the
key viewing positions. A decision has to be made whether to
use brightness or colour to emphasise features: producing highlights
and shadows by the positioning of the equipment, or using light
sources of contrasting colours. (Fig 7) A site survey is almost always
essential to establish the primary viewpoint together with any
secondary positions, and to ensure that the installation does not clash
with existing floodlighting. Care must always be taken to avoid
excessive glare or spill light causing annoyance or hazards. The
appearance of a building in early morning or late evening sunlight,
will often give a good impression of the strength of modelling that
could be achieved by floodlighting.
The direction of light can be used either to emphasise or flatten
detail; panels carved in low relief are best lit with light flowing across
them at a shallow angle, any use of frontal lighting destroys the
details. (Fig 8) Modelling also depends on the position of the viewer,
so the possible directions of view need to be assessed. Silhouette
lighting can be dramatic, conifers, with their dark colour and dense
foliage can be seen to good effect against a lit background. Backlighting of arches, windows sculpture and pinnacles provides rimlighting rather than a solid black silhouette. Where a building has a
decided architectural form, the floodlighting should be designed in
sympathy with it. Buildings with a marked vertical emphasis should be
lit from one side, while the horizontal lines of another design
may demand a frontal or a linear treatment. Well planned
floodlighting can give life to a mediocre building or coherence to a
muddled facade.
The direction of lighting is important for the lighting of areas such
as surface car parks, container parks or industrial storage sites within
the limitations of providing adequate vertical illuminance, the higher
the equipment is mounted the better. Whether masts carrying groups
of powerful discharge lamps in concentrating reflectors (Fig 9) or
single-pole mounted floodlights are used, as the mounting height is
3
Fig 6 Floodlighting at a glancing
angle.
Fig 7 Using contrasting coloured
light sources.
Fig 8 Low relief panels best lit
from a shallow angle.
Fig 9 High mast lighting at a golf
course.
Floodlighting
reduced, the area covered from each lighting position diminishes so that the number of columns is
increased. Also the size of shadows cast by any "obstructions" is effected by the selection of mounting
height and position. The final choice of mounting height and number of lighting positions will depend on
economics, the lighting requirements, site conditions, planning requirements and aesthetic considerations.
Maintenance
A maintenance factor should be included in floodlighting design calculations to allow for a loss of light due
to dirt between cleaning intervals. Fig 10 gives a table from BS5489 to find the appropriate maintenance
factor for outdoor installations. In high illuminance installations the extra cost of towers, cabling, and
floodlights to provide 20 or 30% more light to allow for dirt accumulation can be very great. It is much
better to look for a maintenance factor of between 0.9 and 1.0 by choosing floodlights with good cleaning
characteristics and accepting short cleaning cycles. Cleaning and lamp replacement routines should be
followed to maintain an installation. Maintenance programmes should include lamp replacement,
luminaire cleaning and fault clearance.
The procedure related to which lamps are replaced is a matter of policy, cost and lamp type used. The cost
of replacing lamps on demand (spot lamp replacement) should be compared with that of group
replacement. In making the comparison the following factors are amongst some that should be considered:
• the lamp survival
• the lamp lumen depreciation
• ease of access e.g. extent of signing and coning required on roads
• interference with traffic
• the frequency of luminaire cleaning.
Maintained Illuminance
Adoption of a predetermined maintenance routine can enable the prediction of a design illuminance that
will be met or exceeded during the life of the installation, known as maintained illuminance. This requires
the assessment of an overall maintenance factor that can be used in conjunction with initial lamp lumens
for lighting design calculations. The maintenance factor is made up of components associated with the
luminaire and lamp. The table, below that is from BS5489 part 2 and 3, gives the maintenance factor for
the luminaire, luminaire maintenance factor. The factors for the lamp are the lamp lumen maintenance
factor and the lamp survival factor. These may be obtained from manufacturer’s data. The final
maintenance factor is the product of these factors.
MF = LMF × LLMF × LSF
where:
MF is the total maintenance factor
LLMF is the lamp lumen maintenance factor
IP2* minimum
Pollution Category
LMF is the luminaire maintenance factor
LSF is the lamp survival factor
Degree of protection of lamp housing
IP5* minimum
IP6* minimum
Pollution Category
Pollution Category
Cleaning
interval
High
Medium Low
High
Medium Low
High
Medium
Months
12
0.53
0.62
0.82
0.89
0.90
0.92
0.91
0.92
18
0.48
0.58
0.80
0.87
0.88
0.91
0.90
0.91
24
0.45
0.56
0.79
0.84
0.86
0.90
0.88
0.89
36
0.42
0.53
0.78
0.76
0.82
0.88
0.83
0.87
High pollution occurs in the centre of large urban areas and in heavy industrial areas.
Medium pollution occurs in semi-urban, residential and light industrial areas.
Low pollution occurs in rural areas.
Fig 10 Luminaire maintenance factors
4
Low
0.93
0.92
0.91
0.90
Floodlighting
In the arena of commercial considerations maintenance factors can be
arbitrarily picked to be an unrealistically high figure or even one. By
doing this lighting performance may rapidly go below the
specification after installation, which may not please the client!
Atmospheric losses
Where exterior lighting is achieved by using floodlights, the light will
have to travel through many metres of atmosphere and a factor
which affects illuminances in outdoor installations is the atmospheric
loss caused by air-borne moisture and solid particles. The loss varies
with the time of day, the season, and the location. It also varies with
the mounting height and the length of throw. Losses can be quite high
even when no obvious scattering is occurring. (Fig 11) A typical loss of Fig 11 Taipa Stadium, Macao
illuminance on a clear night in an urban football installation using
four 30m to 45m towers, can be as much as 20 to 30%. In lighting
designs this rarely is taken into account . Illuminance measurements
should not be taken when there is fog or it is raining.
Disability and discomfort glare
Glare is the result of excessive contrasts of luminance in the field of
view. The effect may vary from mild discomfort to an actual
impairment of the ability to see. This is usually caused by viewing a
bright source against a dark background. When the ability to see is
impaired this is called disability glare. At night where there is no
surrounding lighting, when a car comes towards you with main beam
headlights on what you experience is disability glare. Outdoors direct
Fig 12 Milan Hippodrome, Italy
glare from lighting equipment can be restricted in several ways. The
techniques commonly used include careful positioning and aiming of floodlights and other sources of high
luminous intensity. The use of hoods, spill rings and louvres for screening lamps from sight at normal
viewing angles are often used but these will reduce the lighting performance.
Discomfort glare occurs when there is visual discomfort without necessarily impairing the vision of
objects and details. From the practical point of view, the factors affecting glare and the measures that can
be taken to control it are fairly well known. In particular, glare increases as luminaires move closer to the
centre of an observer's field of view, also as the illuminance on the observer's eye increases, and as the
brightness of the background to the floodlights decreases. For an observer within a floodlit area, glare will
be reduced by:
• increasing the floodlight mounting height
• aiming the peak intensity of the floodlights at angles below 70° to the downward vertical
• ensuring that the luminance of the area and its surrounds is as high as possible.
Some compromise is needed on the first two points or the ratio of vertical to horizontal illuminance will
become too low and reduce visibility. The most important single factor to control glare to observers
outside the floodlit area is to limit the intensities outside the actual beam of the floodlight. For observers
both within and outside the illuminated area the location and aiming of floodlights should not coincide
with important directions of view.
There is a CIE report on 'Glare Evaluation System for Use within Sports and Area Lighting'. Calculations
can be made to determine a Glare Rating (GR) that can be compared with recommended glare rating
limits. The version of the Thorn Lighting Vision software that includes exterior lighting has the ability to
calculate GR. In fig 13 the recommended glare rating limits are shown.
5
Floodlighting
Area Lighting
Type of application
Lighting for
Safety and Security
Movement and Safety
Work (*)
GRmax
55
50
45
55
50
45
55
50
45
Low Risk
Medium Risk
High Risk
Pedestrian only
Slow Moving Traffic
Normal Traffic
Very Rough
Rough - Medium
Fine
Sports Lighting
Type of application
Lighting for Training Purposes
Lighting for Competition Purposes
(including CTV broadcasting)
GRmax
55
50
Fig 13 CIE Recommend glare rating limits
Light source colour
Light source colour can be used in two distinct ways. The first way is
to ensure that the colour rendering is suited to the purpose. The
lighting, for example, may have to be sufficiently good to enable
television pictures to be recorded, or colour finishes to be revealed, or
simply to enable vandals and criminals to be recognised easily, directly
or via CCTV. The second way is artistic. Distinct colours of light can
be used to create visually pleasing effects. Coloured light can be used
to differentiate features in a building facade (Fig 14), or to produce an
exciting night-time appearance in a park. The importance of colour
rendering and the performance of the different types of light source
are explained later in this module.
Fig 14 Facade with two distinct
colour light sources.
There are lamps that produce strongly coloured light. The
monochromatic yellow of low pressure sodium lamps is well known
and other strong colours can be obtained from high pressure
discharge lamps. Coloured fluorescent tubes and compact fluorescent
lamps are available. Their efficacy varies widely over the range of
colours. Low wattage coloured PAR reflector lamps may also be
used. The effect of coloured surfaces and coloured light sources is not
very difficult to assess. Unless there is some specific reason for doing
so, the designer would not select sources whose colours differ greatly
from the surface colour. For example, it would be expensive to achieve
an effective result using blue fluorescent lamps to light a dark red
brick wall. The mixing of light from different light sources can be
effective but needs careful design and also the psychological effects of
colour is another factor to take into account. The use of coloured
Fig 15 Colour glass filters.
acetate sheet is not recommended for exterior applications especially
where a long term installation is being planned. Unless protected from the effects of rain and high
temperatures generated by most lamps these materials will suffer. A more permanent solution is the use of
coloured glass filters, mounted to withstand the high temperatures involved. The Contrast range of
floodlights, for example, has the option of coloured glass filters. (Fig 15)
6
Floodlighting
Stroboscopic effects
The light output from most lamps operated from the mains supply fluctuates rapidly at twice the mains
frequency. In some cases this "ripple" is slight and in others it is not. This oscillation can produce a
stroboscopic effect making moving objects appear stationary or moving in a different way to the actual
movement. This can, under certain circumstances, have implications on the safety of lit areas. In sport
where balls or racquets move at high speed the stroboscopic effect can cause errors of judgement. In
practice these effects are seldom a problem, but whenever a significant stroboscopic effect is possible the
lighting should always be designed to reduce such effects. Discharge lamps, their control gear and
electrical supply should be given careful consideration. Where a site is connected to a three-phase
electrical supply, connection of luminaires to different phases may help. This has been successful at
installations where events are televised.
2
V
Floodlighting Equipment
Optical characteristics
The light distribution from floodlights is for convenience classified
into three groups. The general shape of the intensity contours on a
graph identifies these. On the graph the angles from the beam axis in
the vertical (V) and horizontal (H) planes are used as co-ordinates.
(This is a different co-ordinate system to that used for interior
luminaires of elevation and azimuth angles) Fig 16 shows the general
shapes of the three groups that are described as symmetrical,
asymmetrical, and double asymmetrical.
Within each of these patterns there can be varying degrees of light
spread. This is described by angular measurements of the beam. The
beam includes all directions where the intensity of the floodlight
exceeds 10% of the maximum intensity. The beam angle
indicating light spread and is the angular extent of the
beam in the vertical and horizontal planes.
•
For a symmetrical floodlight one figure suffices,
e.g. 60° (or 2 x 30°, implying 30° on either side of
the axis).
•
For an asymmetrical distribution two values are
required, e.g. horizontal 100° and vertical 40°.
H
Symmetrical distribution.
V
H
Asymmetrical distribution.
V
•
For a double asymmetrical pattern three values
are required, e.g. horizontal 100°, vertical above
peak 20°, and vertical below peak 40°
(or horizontal 2 x 50°, vertical 20° + 40°).
In addition to the beam angle, which is concerned with the 10% peak
intensity contour to indicate the 'peakiness' of the lighting within the
beam and the 1% peak intensity contour to indicate where the
effective 'cut-off' of light takes place. Additional data to cover the
optical characteristics of floodlights are the peak intensity, usually
evaluated in candelas per thousand lamp lumens (cd/1000 lm), and the
beam factor, which states what fraction of the lamp lumens are
emitted in the beam. (See section 3 on Floodlighting data and
Calculations)
7
H
Double asymmetrical
distribution.
Fig 16 Light Distribution
Patterns of Floodlights.
Floodlighting
Most reflector profiles are based on the parabola, which
theoretically produces a parallel beam of light. This never occurs in
practice because no source is small enough and no reflector has a
perfectly specular reflectance, in addition to which there are inevitable
tolerances in the reflector profile and the lamp mounting position.
Axially symmetric parabolic reflectors are used for most symmetrical
floodlights and parabolic trough reflectors, with linear lamps, for
most asymmetrical floodlights.
Double asymmetrical floodlights (Fig 17) frequently use compound
trough reflectors, the profiles being made up of a series of parabolas
of different focal lengths. These floodlights sometimes include a strip
of reflecting material above and in front of a linear lamp. This has the
purpose of reflecting light that would otherwise go above the peak
intensity to below the peak intensity. The result is that the light
intensity falls rapidly above the peak intensity, this helps in
controlling glare and spill light.
There are further elements of light control feature in some
floodlights.
• Auxiliary reflectors, mounted in front of the lamp, are used to
direct otherwise uncontrolled forward light from the lamp back
onto the main reflector to improve the beam factor and reduce
spill light.
• External elements, such as louvres, hoods, (Fig 18 & 19) and spill
rings, are used to reduce stray light. (These tend to reduce the
peak intensity and modify the beam pattern.)
• Front moulded glass lenses or stippled diffusers to enable a
variety of light distributions from one narrow beam floodlight.
(Fig 21 & 22)
Fig 17 Double Asymmetrical
Floodlight.
Fig 18 Combined external louvre and
hood to floodlight.
A distinction is often made between area and precision floodlights.
Area floodlights, for example fig 20, provides a wide light distribution
for covering large areas, whereas precision floodlights (fig 22) are
associated with narrower beams with low levels of spill light. A range
is usually offered so that a choice can be made on the optical
characteristics.
Fig 19 External hood fitted to
Floodlight.
Fig 20 Areaflood 40.
Fig 21 Front moulded glass lens on
Contrast Pinspot floodlight.
8
Fig 22 Front moulded glass lens on
CSI Series floodlight.
Floodlighting
Columns, masts and towers
The range of heights for columns or masts is typically 4-30m for
mounting luminaires outdoors. At heights of up to 12m there is a
strong case for the use of columns, between 12 m and 30m the choice
depends on the quantity of equipment to be supported and above 30m
towers or heavy duty masts are used.
Columns
Lighting columns are made of aluminium, steel and concrete.
Aluminium has the advantages of lighter weight and a natural
resistance to corrosion, even in atmospheres heavily laden with salt or
chemicals. All columns are generally available in 5, 6, 8, 10 and 12m
heights with provision being made to accommodate control gear,
mounted on a wooden base-board, in a locked compartment at the
bottom of the column. Some of the types of metal column available
are:
• Flange plate mounted
• Root mounted
• Raising and lowering type (Fig 24 & 25)
• Hinge type
The foot of a metal column is coated internally and externally with
bitumen over the whole of the planted depth and to 50mm above
ground level. Columns above 12m, for example 16-20m, are normally
of the raise and lower variety. The column is hinged at its base and is
raised and lowered by the use of a jack frame assembly. Many column
designs are available and a type should be chosen that is in keeping
with the surroundings.
Fig 23 Sports stadium with
PRT2000 floodlights on towers.
Fig 24 Raising and lowering
column.
When siting lighting columns near trees the following points must be
considered:
•
•
easy access to maintain the installation e.g. for cleaning, painting
and relamping; and
problems arising from the future growth of the tree obscuring the
light.
Masts
Fig 25 Base of raising and
Masts are used extensively in large areas, such as docks and lorry
parks, at heights up to 30m. The luminaires are mounted on a cradle. lowering column.
Special raising and lowering gear consisting of a system of steel cables
carried inside the mast move the cradle by means of a portable winch at ground level. Masts above 50m are
normally accessed by means of an internal ladder with the luminaires mounted on a headframe.
A lattice tower may be an economic alternative to a single mast, its aesthetic disadvantage being
compensated by its ability to carry a greater number of floodlights and by the versatility of the various
types of head platforms.
Adequate foundations are necessary, and all structures must be able to withstand the wind forces likely to
be experienced. The specification of foundations is the domain of structural engineers, this is not
something that lighting designers need to do. What lighting manufacturers can provide is data on the
weight and wind area of luminaires, known as 'windage'. This data and data about the mast structure and
geographical location can enable checks to be made that the system is within the safe limit. If the limits are
exceeded there is the possibility that the column or mast may deform or collapse in high winds.
9
Floodlighting
Lamps
A resume of lamp types is given here to assist in determining the
differences and advantages of each type.
Although comments are included on lamp life, this is an involved
subject because life expectancy and light output is often related to the
type and frequency of use. For example most sports applications
require the lamps to be switched on and used for two hours then
switched off. Alternately an industrial application will require the
lamps to be switched on at dusk and switched off at dawn for an
operational period of 10 hours. This is quantified in terms of
switching cycle, the industrial application would have a 10-hour
switching cycle. The 2-hour switching cycle may age lamps at a rate
three times greater than the 10-hour cycle. For this reason there is a
significant move to quantity lamp life and performance in terms of
switching cycles providing three set of data for 2-hour, 4-hour and
10-hour giving average life and lumen maintenance.
Fig 26 Metal halide (elliptical and
tubular)
Discharge lamps
Metal halide (elliptical and tubular) (Fig 26) - All metal halide lamps
operate a discharge in mercury vapour with metallic additives,
enclosed in a quartz tube. The metallic additives are introduced as
halide compounds that control the dosing and ensure that the metallic
elements mix well with the mercury vapour. There is an outer glass
bulb, which for some lamps, is internally coated with a phosphor to
modify the spectral characteristics of the light emitted.
Fig 27 Metal halide (linear double
ended)
These lamps are suitable for lighting events that are televised when
the appropriate illuminances are provided.
Good to very good colour rendering. There is a wide range of
efficacy, colour appearance and colour rendering.
A suitable enclosed luminaire must be used for these lamps. (There
are a few exceptions to this.)
Fig 28 Metal halide (MQI)
Metal halide (linear double ended) (Fig 27) - These lamps are available in
wattages of 750W to 2000W. There is no outer glass bulb, the
floodlight itself acts as an enclosure. Precision optical design can be
used with linear lamps. A typical application is for sports stadia.
Metal halide compact - There is a wide range of compact metal halide
lamps, for example Phillips CDM and GE Lighting CMH ranges.
There provide colour appearance in the 3000K to 4000K range with
again very good colour rendering. (Fig 28) There is also White SON.
This is a hybrid of high pressure sodium lamp technology and metal
halide. Metal halides are introduced into a high pressure sodium arc
tube. The result is as the name suggests a much whiter colour, a
higher colour temperature, than high pressure sodium.
Fig 29 Compact source iodine
(CSI)
Compact source iodide (CSI) (Fig 29) - The light source and PAR 64 sealed beam reflector are built into one
assembly for this 1kW lamp. The colour rendering is very good. Suitable for floodlighting televised
events. There are hot re-strike versions that come to full brightness rapidly after an interruption in the
mains supply.
10
Floodlighting
High pressure sodium (elliptical and tubular) (Fig 30) - With high
pressure sodium lamps a discharge operates in a sintered alumina arc
tube contained in a glass bulb, either elliptical or tubular. This is a
high efficacy light source that gives long life while maintaining the
lumen output well. The warm coloured light allows some colour
discrimination but not accurate colour rendering. As the arc tube is
small fairly precise optical control can be achieved by suitable
luminaire design with the tubular lamps. Elliptical lamps usually have
an internal coating of diffusing material on the bulb.
These lamps are suitable for area floodlighting, car parks, security
lighting but compatibility with CCTV cameras may need checking.
Improved colour rendering high pressure sodium lamps raise the
colour rendering into the good category, although the colour
appearance remains warm. They are available in elliptical and tubular
lamps.
Fig 30 High pressure sodium
(elliptical and tubular)
There is a wide range of lamp wattages: 50W - 1000W.
Filament Lamps
Linear tungsten halogen (Fig 31) - A tungsten filament is supported
between molybdenum foils connected to contacts in ceramic end caps
at each end of a slim quartz enclosed tube. The gas filling inside is at a
higher pressure than GLS lamps and includes halogen, which
regenerates the loss of tungsten from the filament that also operates at
a higher temperature. The lamp provides a whiter light and improved
efficacy over the GLS lamp. The colour rendering is excellent. Unlike
high pressure discharge lamps full light output occurs on switch on.
Fig 31 Linear tungsten halogen
Care should be taken not to contaminate the outside surface of the
quartz bulb with grease from fingers marks. If this does happen,
before switching on the lamp, clean with a soft cloth moisten with
white spirits.
There is a wide range of lamp wattages: 100W - 2000W.
Fig 32 Compact tungsten halogen
with dichroic mirror reflector
Compact tungsten halogen - Small capsules of quartz contain a small tungsten filament again with a halogen
high pressure gas filling. Many have an integral dichroic mirror reflector that reflect light but transmit
heat (Fig 32). A variety of compact tungsten halogen lamps are used in mini-floodlights, some operating at
low voltage and others at mains voltage. A selection of beam angles is offered.
Other Lamps
High Pressure Mercury - This lamp is used for low initial cost where colour rendering is not a major factor.
The colour rendering is poor and the lumen maintenance is not high. It is used in streetlighting where a
white light is required.
Tubular and Compact Fluorescent - There are now some floodlights that use compact fluorescent lamps,
suitable for small areas. They give longer lamp life than tungsten halogen and can give good colour
rendering.
Low Pressure Sodium - This lamp is widely used for street lighting but little used for floodlighting. The
large lamp size makes it difficult to provide optical control and together with the non-existent colour
rendering does not make it very suitable.
[Refer to lamp manufacturer's catalogues for all detailed lamp performance.]
11
Floodlighting
Ignitors and transformers
Discharge lamps that require a higher voltage than that of the
mains supply may be started by electronic ignitors or step-up
transformers. Ignitors generate a series of high-voltage pulses that cease
Ballast
when the lamp starts. The pulses are of short duration and, because
of capacitive attenuation, the length of cable between ignitor and lamp
is limited. Some ignitors include a pulse transformer inside the ignitor
can, and the cable limit does not usually exceed 2m, while others use a
tapping on the ballast, or the whole of the ballast winding, to produce a
pulse or pulses. The following table can be used to find the
maximum recommended cable length for a particular cable type between
a lamp and ignitor. To find the maximum cable length the "maximum
cable capacitance" given against each lamp type later in this module
is divided by the "capacitance per metre for calculating cable length"
in the table. The insulation of the cable must be able to withstand the
high voltages generated, limited by international agreement to 4.5kV,
Power Factor
standard 1000V insulated cables are suitable. Mineral insulated cables
Correction
should not be used in ignitor circuits, as transient voltages will exceed
Capacitor
the voltage rating of that cable.
Capacitance of typical PVC cables
PVC Insulated cable type 1.0 to 4.0 mm2
Unsheathed single cores, loose packed
(2 cores) in earthed 20mm conduit
Unsheathed single cores tight packed
(8 cores) in earthed 20mm conduit
Twin and earth flat section (loose contact
with earth)
Twin SWA (armoured or sheathed)
Multicore SWA (armoured or sheathed)
Multicore non armoured
Ignitor
Capacitance per metre
for use in calculating
cable length (pF/metre)
70
120
115
300
300
300
Fig 33 150W HPS lamp circuit
with components.
Other circuits may utilise a high starting voltage, which is produced by the ballast itself and takes the form
of a high reactance autotransformer. The magnetic coupling in the windings is designed so that, when the
lamp has started, the transformer behaves solely as a current limiting device.
Fuse ratings
The fuse rating of high pressure discharge lamps is dealt with first and then the fuse rating of low pressure
sodium lamps. The correct fuse for a high pressure discharge lamp, is determined by the starting
condition, when higher than normal supply currents will flow. Three current conditions must be allowed
for:
• Capacitor inrush current
• Current due to rectification
• Run-up current
Capacitor inrush current
The initial charging current taken by the power factor correction capacitor (fig 33) depends on the
impedance of the supply lines and wiring, and the instantaneous value of the supply voltage when the
switch is closed. This transient current can be up to 25 times the normal capacitor current but only lasts
for about a millisecond. To allow for this it is recommended that fuses supplying circuits
containing capacitors should be rated at 1.5 times the normal capacitor current. (The normal capacitor
current at 230/240V 50Hz is the capacitor value in µF multiplied by 0.076A).
12
Floodlighting
Current due to rectification
For a short period after starting a discharge lamp may act as a partial rectifier. This occurs when the two
electrodes warm up at different rates, the hotter one emitting more electrons when it is acting as a cathode
than the cooler one which becomes a cathode in the subsequent half cycle. As there is more current
flowing in one direction than the other there is partial rectification and a DC current will flow. The effect
of this DC is to saturate the iron core of the ballast and reduce the impedance allowing a current of several
times the normal value to flow. This condition may last for a few seconds until stable hot spots are formed
on both the electrodes. This can often be seen immediately after switch-on when the lamp flickers
noticeably before stable hot spots are formed. It must be emphasised that this transient condition does not
always happen and that the degree of partial rectification will vary from lamp to lamp and from time to
time.
Starting current
After the initial starting period there is a run-up time of several minutes during which the lamp and supply
current will fall from as much as 150% to 100% of normal value. The maximum value of the supply
current that flows during the first minute is referred to as the supply starting current and is given in
Table 1 with each lamp type later in this section. This does not include the current due to rectification or
the capacitor inrush current. Until the lamp is fully warmed up the volt drop across the lamp will be low
allowing a higher than normal running current to flow. As the lamp warms up the vapour pressure will
increase, and with it the lamp voltage, until steady stated conditions are achieved. These conditions occur
every time a lamp starts, unlike the current due to partial rectification, which is random. The normal
supply current when full run-up is also given in Table 1.
Fuse ratings for single lamp circuits
Table 2 with each lamp type later in this section, gives the recommended fuse ratings for a single lamp
circuit. These values are based on possible rectification currents that will not always occur, but need to be
allowed for.
Fuse ratings for installation of more than one lamp
Where several lamps are supplied through a common fuse it can be assumed that only some of the lamps
will rectify on starting. The rated fuse current per lamp can therefore be reduced considerably from the
single circuit value. Starting current and capacitor inrush current predominate and are used to calculate
the fuse rating.
Table 2 with each lamp type also gives recommended HBC fuse
ratings for up to six lamps. Where more than six lamps are installed
the fuse rating should be calculated by multiplying the starting current
given in Table 1 by the number of lamps concerned. If the calculated
rating is less than the recommended fuse for six lamps, then the higher
value should be used as given in Table 2. The fuse rating must then be
checked to ensure that it can deal with the capacitor inrush current.
To do this it must be not less than 1.5 × the total normal capacitor
current. (The current taken per µF at 230/240V 50Hz is 0.076A.)
Recommended fuse and MCB types
The fuse ratings given with each lamp type later in this section are
based on the assumption that fuses to BS 88 (Industrial HBC
Fuses) will generally be used. The ratings quoted are preferred sizes
from BS 88. The same ratings can generally be applied to Type C
MCBs (Miniature Circuit Breakers) although some very fast acting
devices may trip due to capacitor inrush current if the source
impedance is very low and the instantaneous supply voltage on
switching is near the peak value. Type B MCBs are not recommended
for discharge lighting circuits, as the instantaneous trip current value
may be too low.
13
Fig 34 Multiple high pressure
sodium lamp installation
Floodlighting
Worked example
An installation of twelve 250W HPS lamps, all on the same phase, switched in four groups of three
lamps. From Table 2, the three lamp final circuit can be controlled from 16A HBC fuses. The sub-main
fuse will control twelve lamps. The run-up current given in Table 1, is 1.5A so a minimum fuse rating is
12 x 1.5 = 18A, say 20A. To check the power factor correction capacitor current, 30 µF is used with a
250W HPS circuit so the total amount of capacitor current for 12 circuits will be:
12
= 27.4 A
× 30
× 0.076
(Capacitor
(No. of ×
× (Current per
µF)
value in µF)
circuits)
Recommended fuse = 1.5 × total normal = 1.5 × 27.4A = 41A capacitor current
Bearing in mind that cable sizes are calculated from the fuse rating it would be reasonable to use a 40A
fuse in this case. The normal running current for a 250W HPS circuit is 1.3A, giving a value of only 15.6A
for a 12 lamp circuit installation. The above example shows that a 40A fuse is necessary in this case. This
clearly illustrates the point that the value quoted for the normal running current, or even that quoted for
the starting current should not be used when calculating fuse ratings.
High pressure mercury lamp circuits
There is a reduction in lamp power due to the effect of cable runs between high pressure mercury lamps
and ballasts. For circuits that do not employ starting devices such as electronic ignitors the only effect of
long cable runs is to introduce extra resistance into the circuit with the consequent reduction in
lamp current, power and light output. The following empirical relationship has been established for high
pressure mercury lamps to determine the percentage of nominal lamp power:
187 × I × R × Vl
Pl = 100 %
Vo2
where:
Pl is the lamp power in watts
I is the nominal lamp current
R is the cable resistance in ohms
Vl is the nominal lamp voltage in volts
Vo is the ballast open-circuit voltage in volts (mains voltage in the case of simple choke circuits)
TABLE 1
Supply current at 230/240V 50Hz using standard Thorn gear including recommended power factor
correction (PFC) capacitor.
High Pressure Mercury Lamps
Lamp power (W)
50
80
125
250
400
700
1000
PFC capacitor (µF)
6
8
8
13
20
20
50
Supply starting current (A)
0.32
0.5
1.1
2.2
4.0
6.5
9.0
Supply running current (A)
0.3
0.4
0.7
1.33
2.2
3.5
5.0
TABLE 2
Recommended fuse (HBC or MCB) ratings (A) for multiple lamp installations for 230/240V 50Hz
supplies.
High Pressure Mercury Lamps
Number of Lamps
1
2
3
4
5
6
50W
4
4
4
4
4
4
80W
4
4
4
4
6
6
125W
4
4
6
10
10
10
250W
10
16
16
20
20
20
400W
16
20
20
25
25
25
700W
16
20
25
32
32
40
1000W
20
25
32
40
50
63
14
Floodlighting
Metal halide and compact source iodine circuits
Metal halide lamps have similar electrical characteristics to high pressure mercury lamps but require
higher voltages for starting. During run-up, high re-ignition lamp voltage peaks can occur, and the lamps
will extinguish if the ballast circuits provide insufficient sustaining voltage. The additional starting voltage
is obtained from transformers, from resonant circuits, or from ignitors which produce transient or regular
pulses. The voltage pulses must have high energy to enable the transition from glow to arc discharge to be
made quickly.
Maximum cable capacitance for MBI, MBIL and CSI circuits
Lamp
Watts
Ignitor
MBI-T Arcstream
MBI
MBIL
CSI
150
250
400
1000
1500
1000
G53459
G53455
G53455
G53342
G53342
G53444
Maximum cable
capacitance (pF)
150
100
100
18500
15500
50
TABLE 1
Supply current at 230/240V 50Hz using standard Thorn gear including recommended power factor
correction (PFC) capacitor.
Metal Halide MBI Lamps
Lamp power (W)
150
250
400
PFC capacitor (µF)
20
30
25
Supply starting current (A)
0.76
1.5
3.5
Supply running current (A)
0.76
1.3
2.0
TABLE 2
Recommended fuse (HBC or MCB) ratings (A) for multiple lamp installations for 230/240V 50Hz
supplies.
Metal Halide MBI Lamps
Number of Lamps
1
2
3
4
5
6
150W
4
6
10
10
16
16
250W
10
16
16
20
20
20
400W
16
20
20
25
25
25
Low pressure sodium lamp circuits
Low pressure sodium lamps are cold started using voltages generated by leakage reactance transformers or
electronic ignitors. The 35, 55, 90W ignitor circuits enable a smaller choke ballast to be used, together
with a smaller power factor correction capacitor.
In recommending fuse values for low pressure sodium lamps it is necessary to distinguish between
transformer ballasted circuits with large power factor correction values and choke/ignitor circuits. For
single lamp circuits, the normal supply current for ratings up to 135W in both cases are less than 1 Amp so
the use of a 4A BS 88 fuse or Type C MCB which is the smallest practical rating will adequately cover
capacitor inrush and the lamp rectification currents. The steady supply current at starting with these lamps
is less than the normal running current for both types of ballast. For multi-lamp circuits, the fuse rating
will be dictated by the capacitor surge currents.
There is an effect on low pressure sodium lamps due to the cable run between the lamps and ballasts. SOX
lamps exhibit negligible change in lamp power with change in cable resistance - this is because a reduction
in lamp current leads to a compensating rise in lamp voltage. However, for satisfactory lamp operation,
cable resistance must not be allowed to reduce lamp current too severely. This should not present
15
Floodlighting
problems in the majority of practical situations (e.g. 80 ohms of cable resistance will reduce lamp current
by, an acceptable, 10% whilst at the same time reducing power by only 2%).
SOX lamp maximum cable capacitance for ignitor circuits
Lamp
Watts
Ignitor
SOX
35
55
90
G53311
G53421
G53456
Maximum cable
capacitance (pF)
20000
20000
20000
Recommended fuse rating (in Amps) for multiple lamp installations for 230/240V 50Hz supplies.
SOX Lamps
Number of Lamps
1
2
3
4
5
6
18W
4
4
4
4
4
4
35W
4
4
4
4
4
4
55W
4
4
4
4
4
4
90W
4
4
4
4
6
6
135W
4
10
10
16
20
25
HPS lamp circuits
High pressure sodium (HPS) lamps have similar electrical characteristics to high pressure mercury (MBF)
lamps but the more rapid de-ionisation gives a delay in re-ignition every half cycle and leads to a poorer
lamp power factor and a lower arc tube voltage than with MBF lamps. This prevents HPS and MBF lamps
of similar wattage from being interchangeable. HPS lamps can be controlled by a choke but require an
ignitor to provide high voltage, low energy, starting pulses and to ionise the fill gas and allow a mains
voltage derived arc to start the discharge. The E in a triangle mark on HPS lamps signifies that they
require an external starting device and are used only in circuits which include an ignitor. Thorn ignitors
operate in conjunction with a ballast having ignitor "tappings" - the ballast output terminal and the ballast
insulation possessing the necessary electrical insulation strength to withstand the ignitors pulse.
TABLE 1
Supply current at 230/240V 50Hz using a standard Thorn gear including recommended PFC capacitor.
High Pressure Sodium Lamps
Lamp power (W)
50
70
100
150
250
400
1000
PFC capacitor (µF)
8
10
12
20
30
40
85
Supply starting current (A)
0.35
0.55
0.7
0.7
1.5
3.0
6.0
Supply running current (A)
0.3
0.4
0.5
0.8
1.3
2.2
5.4
TABLE 2
Recommended fuse (HBC or MCB) ratings (A) for multiple lamp installations for 230/240V 50Hz
supplies.
High Pressure Sodium Lamps
Number of Lamps
1
2
3
4
5
6
50W
4
4
4
4
4
4
70W
4
4
4
6
6
10
100W
4
4
4
6
10
10
150W
4
6
10
10
16
16
250W
10
16
16
20
20
20
400W
16
20
20
25
25
32
1000W
20
25
32
40
50
63
16
Floodlighting
High pressure sodium lamp maximum cable capacitance
Lamp
Watts
Ignitor
HPS
50
70
100
150
250
400
1000
G53353.4
G53353.4
G53455
G53282/B
G53282/B
G53282/B
G53316
Maximum cable
capacitance (pF)
700
700
100
2750
2500
2000
100
Voltage Variation
Lower voltages affect a floodlighting system. The further away floodlights are from the switchroom the
greater the voltage-drop. This results from resistance in the supply cables. Therefore voltages can fall
below the nominal figures on which the manufacturer's data is based.
The light output from some discharge lamps may vary at a rate four times greater than the applied voltage.
That is to say 1% voltage reduction can produce a 4% reduction in light output. This can have a
significant effect and may have to be overcome by increasing the number of floodlights. These factors
should be considered in the initial design stages where the lighting engineer should be aware of the supply
cables and respective voltage reductions so that the system may be designed accordingly. The lighting
equipment supplied should be able to compensate for such voltage variations, and this can normally be
achieved by providing a range of voltage connections on the ballast transformer of each floodlight.
The supply voltage should also be checked at a time of peak demand
during a period when the floodlighting is likely to be used before the
system is designed, so that an accurate assessment of the operating
voltage can he made.
This research may be carried out by an independent consulting
engineer or by the design engineer of the local electricity board. The
maximum spare capacity will need to be determined, together with the
resistance of the installation at the supply terminals. The resistance
can be measured with an earth loop impedance tester, and once this is
established the additional voltage reduction at the supply point may
he calculated for the new floodlighting load.
From these tests additional calculations will be made to determine the
fault rating of the installation at each point from the supply terminals
to the furthest structure. The fault rating is the maximum power that
may be generated under a fault condition or short circuit. With this
information the protective switchgear is assessed to determine if it will
safely contain this fault current, and also disconnect the circuit within
a safe period of time.
Such calculations are now a requirement of the latest edition of the
IEE wiring regulations (16th edition), and will ensure the safety and
adequacy of the design.
Fig 35 Sets of control gear are
slide up the column base.
17
Floodlighting
Control gear housings
Banks of gear mounted remotely in one enclosure should have
ballasts spaced 150mm apart in all directions and be adequately
ventilated while gear operating at a surface temperature of 80°C or
over should be enclosed in incombustible material (i.e. a metal gear
box). Wherever possible control gear should be mounted close to the
lamp or lamps, in the luminaire itself, in the base compartment of the
column or in a rainproof control box. Large tower and mast
installations usually require the provision of a locked cubicle in which
all the gear, except ignitors, is housed. This is normally placed at the
base of the tower and is specified and supplied by the electrical
contractor. It is important to mount choke and ballasts away from
equipment that is sensitive to heat and to design for adequate
ventilation of both internal and external cubicles, allowing a free
passage of air through them. The tw rating of the ballast and the tc
rating of the capacitors should not be exceeded for full gear life. They
must not be mounted on or near combustible surfaces.
A typical ventilated weather proof control gear cubicle with metal
or fibreglass casing is illustrated. (Fig 36) The front and back panel
should be hinged or removable for access. Heat sensitive components,
such as capacitors and switches should be mounted as low as possible.
Air vents at the base should be equivalent to 50-60% of the plan area
and a slot at least 15mm wide should be provided all around the top.
These vents may be covered with wire gauze, the obstruction of which
should be taken into account. The overhang of the roof should be
designed to prevent water running back under the edge. Where the
public has access to the bases of towers the use of wire armoured
supply cable will provide reasonable protection, also the cubicles must
be kept locked. Where there is protection from the weather and no
public access, control gear may be mounted on open racks.
Questions 1
Chokes
Capacitors & switchgear
Fig 36 Control Gear Housing for
an outdoor installation
Fig 37 Switchroom with control
gear
1.
For an area 50 × 200m what number of grid points for horizontal
illuminance calculations would you use?
2.
If the primary viewing position of a facade with strong vertical features is in front of the facade, what
positions and direction would you first consider for floodlighting and why?
3.
What glare rating does the CIE recommend for televised sports events.
4.
What external items can be added to floodlights to give additional light control?
5.
What is the maximum cable length for 2.5mm2 twin and earth flat section cable between an ignitor
and a 400W HPS lamp?
6.
What type and current rating MCB is suitable for four 400W metal halide lamps?
7.
Why is it important to know the actual supply voltage for large floodlighting projects before
installations?
8.
What lamp performance information would be valuable when designing a lighting scheme for a
football stadium?
18
Floodlighting
3
Floodlighting data and
calculations
There are several ways of presenting
photometric data for floodlights. The simpler
methods of presentation are dealt with here.
For preliminary design work the beam data is
particularly useful, fig 38 shows an example
for an Areaflood 40. (Fig 20)
Peak intensity (I) cd/klm
Beam factor to 10% peak (I)
Beam angle to 10% peak (I)
1110
0.74
Horizontal
Vertical
Horizontal
Vertical
Horizontal
Vertical
Beam angle to 50% peak (I)
Beam angle to 1% peak (I)
The peak intensity is in a direction 21° to the
normal of the front glass of the floodlight
expressed in cd/klm. To obtain the actual
intensity in cd the value, in this case, 1110
needs multiplying by the bare lamp lumens
Fig 38 Beam data.
divided by 1000.
The beam factor to 10% peak is the decimal of the lamp
flux in the beam to where the intensity is 10% of the peak
value. This can be thought of as how much of all light from
the lamp goes into the beam. This can be referred to as BF
for beam factor.
The beam angle to percentage of peak is measured in a
horizontal and vertical plane with respect to the peak
intensity. (Fig 39) The horizontal angle is doubled because
the angle is either side of the central peak intensity. The first
vertical angle is above the peak intensity and the second
vertical angle is below the peak intensity.
2 × 50°
36°/66°
2 × 39°
7°/13°
2 × 67°
49°/89°
I peak
21°
Elevation (vertical)
1
10
Plan (horizontal)
Ipeak
Ipeak
1
10
Ipeak
1
10
Ipeak
1
10
Ipeak
Ipeak
Fig 39 Beam angles.
The beam angle to 10% peak indicates the angular spread of
the useful beam. The beam angle to 50% peak is useful for
those occasions when beams from two of the same type of
floodlights overlap with the intention of giving an even ‘wash’
of light. The beam angle to 1% peak is the boundary beyond
which there is just spill light, that will make no useful
contribution to the lighting scheme.
The intensity curves for a floodlight graphically shows the
lighting performance. (Fig 40) The most of the data given in
the beam data can be read from these curves. For the
intensity in candelas multiply the intensity by the bare lamp
lumens divided by 1000. The solid curve denotes the intensity
in the horizontal plane. The dashed line denotes the intensity
in the vertical plane, positive angles are above the peak
intensity. All angles are measured with respect to the peak
intensity, which may not be normal to the front glass of the
floodlight, but should be defined.
Fig 40 Intensity curves.
The lighting performance of a floodlight can be evaluated by
looking at an isolux diagrams when it is available.
(Fig 41) The format is similar to that for amenity luminaires. For a specified mounting height, on a grid in
metres contours of constant illuminance are shown in units of lux/1000 lm. To obtain an actual value of
illuminance just multiply by the bare lamp lumens divided by 1000. The isolux diagram can be used to
19
Floodlighting
assess the illuminance created when the floodlight is mounted
at other mounting heights, by using the same conversion
factors given for amenity luminaires:
Multiply contour values by:
(Stated mounting height in m)2
(New mounting height in m)2
Multiply grid distance by:
New mounting height in m
Stated mounting height in m
The boundary of the area to be lit will not necessarily
coincide with the area covered by the floodlights, like in the
case of a tall narrow building, or one with a complicated
profile, a considerable amount of light may be wasted.
(Fig 42) This situation can be accounted for by what is called
the Waste Light Factor, WLF although it would be more
appropriately called the What’s Left Factor. More light may Fig 41 Floodlight isolux diagram.
be wasted on a tower or chimney than on a rectangular
building or advertising hoarding. The Waste Light Factor is
the decimal of light that gets onto the object being lit, not the
Waste light
decimal of what light is wasted. Under favourable conditions a
waste light factor of 0.9 might be assumed, but in difficult
situations it may be reduced to 0.5 or lower. This factor when
multiplied by the Beam Factor, BF gives the Utilisation
Factor, UF :
UF = WLF × BF
The lumen method of design can then be applied, as with
interior lighting design:
N × F × UF × MF
E=
A
where:
E is the average maintained illuminance
N is the number of luminaires
F is initial bare lamp lumens per luminaire
UF is the Utilisation Factor
MF is the Maintenance Factor
A is the area to be lit
Even more simply at the first stage of design calculations it is
common practise to use an estimated utilisation factor of 0.3.
This figure is low for asymmetric and some symmetric
projectors giving precise light control and too high for wide
angles projectors that will project light beyond the boundaries
of the area being considered.
Fig 42 Waste light floodlighting facade.
If a rectangular area is to be lit the Thorn Floodlighting Calculator is a better choice for preliminary
designs than using a UF of 0.3.
Floodlighting calculations
The designs of many decorative floodlighting schemes rely for success on a combination of aesthetic
appreciation, experience, intuition, and flair. However, the majority of exterior lighting installations,
certainly for the floodlighting of functional areas, succeed by satisfying the various lighting criteria,
following a design process normally consisting of three stages:
20
Floodlighting
•
An assessment is made of where to locate the floodlights, the type of light distribution required, and
the light source characteristics that suits the particular application.
•
A lumen calculation is carried out to find the number and loading of the lamps to achieve the
required average illuminance.
•
When necessary, point-by-point calculations are done to determine the aiming pattern of the
floodlights for the required uniformity.
The third stage may modify the earlier calculations, and is the stage when the use of a computer becomes
invaluable for large and complex installation.
Layout & mounting height
The major problem at the initial stage of designing a floodlighting installation is that there are so many
possible variables. Unlike interior lighting, where the boundaries of are clearly defined by walls and ceiling
and floor, floodlighting equipment can be placed within the area to be lit or located on columns well
outside the area. The height of the columns and their distance outside the area will have to be considered
because, until such matters are decided, it is
impossible to tell what beam distributions
are required or how the floodlights should be aimed.
10°
The best advice for anyone starting on a design is to
H 53°
start by studying the characteristics and limitations
of the site. With areas of regular shape and with set
1.3H
dimensions, such as sports areas, standard pole
layouts may be available to guide the designer, but
2H
this is rarely the case with industrial and commercial
areas.
Generally the higher the mounting height, the
smaller is the number of columns, masts, and towers
required. As a result a higher mounting height
generally achieves the most effective and efficient
floodlighting at the lowest installation cost, but the
relationship between mounting height H and the
depth of the area to be lit D is important.
If an open area is to be lit from one side (shadows
permitting), the ratio D/H should not be greater
than 5. If there are obstructions within the area,
such as in a stock yard, then the ratio should be
reduced to 3 or even 2 with extensive obstructions
(the ratio also gives the ratio of shadow length to
object height at the far edge). When lighting from
two or more directions, the ratio can be increased to
6 but should be reduced to 4 if there are
obstructions.
In the initial design the peak intensity of the
floodlight is usually directed to a point some two
thirds of the way across the depth of the area.
Floodlights with double asymmetric light
distributions can provide vertical beam spreads
suitable for different D/H ratios, but such
floodlights have wide horizontal distributions.
Where D/H exceeds 3 it is often necessary to use a
Fig 43 Typical floodlight aiming for area 2H wide
99°
H 63°
2H
3H
Fig 44 Typical floodlight aiming for area 3H wide
76°
H
H
55°
4H
6H
Fig 45 Typical floodlight aiming for area 6H wide
from both sides
21
Floodlighting
supplementary floodlight with a wide vertical beam
angle aimed at a lower elevation to fill in the area
close to the base of the column. If floodlights with
symmetrical light distributions are used to illuminate
very large spaces a series of projectors are used.
Those aimed at high elevations have narrower beam
angles than those aimed at lower elevations.
H
S = 2H
2H
Spacing
SHR = 2
The spacing between columns, when areas are to be
lit from one or two sides may be dictated by site
Fig 46 SHR in range of 1.5 to 2 are common
limitations. Given no constraints, the spacing
to height ratio (SHR) is determined primarily by the
horizontal beam spread of the floodlights, selected in the first place because of their vertical beam
characteristics.
Values of SHR in the range 1.5 to 2.0 are commonly used with asymmetrical floodlights: values over 3 are
unlikely to provide acceptable uniformity. Where higher SHR values prove to be necessary because of site
constraints, some floodlights may have to be aimed at points which do not lie on a transverse line from
their column or a more complex aiming pattern of symmetrical floodlights may have to be used. It will be
necessary to check the consequences of the aiming pattern on both illuminance and uniformity by a pointby-point calculation.
Zonal flux diagram
If they are available for the range of floodlights being considered, zonal flux diagrams provide a more
accurate and yet easy way of determining utilsation factors for floodlighting schemes. A particular system
of angular scaling is used for floodlight photometric data, for plotting isocandela contours and evaluating
zonal flux values. (See fig 48) The right-hand side of the Isocandela and zonal flux diagram is the zonal
flux diagram for one-half of a 150W Areaflood 15 floodlight. The number in a particular grid square is
the flux emitted per thousand lamp lumens in the zone defined by the two pairs of vertical and horizontal
angles forming the grid square. The total flux emitted by the floodlight is equal to twice the sum of all the
flux values shown, indicating that for this particular floodlight 2 x 339 = 678 lm for every 1000 lm of bare
lamp flux. The dotted line is the contour for 10% of the peak intensity, thus identifying the beam. An
overlay representing the area to be illuminated can be expressed in vertical and horizontal angles
and placed over the diagram. Also the overlay can be moved up and down to account for elevational
adjustments of the floodlight. For azimuth adjustments redrawn overlays are required. The use of the
diagram is best illustrated by an example.
Fig 47 shows a 20m x 20m area that requires lighting. An Areaflood 15 floodlight is being considered, on
an 8m pole located on the edge of the area as
indicated. A typical aiming point is selected
A
for the floodlight of 60° elevation.
With this layout the overlay to be prepared
requires two areas to be plotted on it, to the
right and left of the pole. The aiming
point plots on the vertical-horizontal grid
(V,H) as co-ordinates (0°,0°). The area
boundaries BC and AD plot as horizontal
lines. A line drawn across the area through
the aiming point corresponds to the chosen
elevation angle of 60° from the vertical. The
line BC, at the base of the column, will
therefore be 60° below the peak intensity
aiming angle. From trigonometry the line
B
O
X°
10m
8m column
W°
F
Z°
Y°
P
E
G
10m
20m
C
Fig 47 Geometry of 20m x 20m lit area
22
D
Floodlighting
Fig 48 Thorn standard format for floodlighting data
23
Floodlighting
AD is worked out at 68° from the vertical, and therefore is 8° above the peak intensity aiming angle
(68° - 60° = 8°). The lines CD and BA when projected onto the diagram form a curve, however for most
practical designs a straight line is assumed for CD and BA, or with a degree of refinement two straight
lines. The horizontal angle X corresponding to the line EC is determined by trigonometry is 51°. Likewise
the angle W is found to be 25°. (Fig 49)
These horizontal angles can be plotted on the zonal flux diagram as shown. Thus an approximate mapping
of the area, as seen from the floodlight, can be determined. This overlayed mapping can now be used to
estimate the utilisation factor by adding up all of the numbers that fall within the area, an estimation being
made for any zones that do not lie completely within the area. The total value, the sum of both sides, will
need to be divided by 1000 to give the utilisation factor, since the data is based on 1000 lamp lumens. In
fig 50 the sum for one side is 161, giving a total of 322 so the utilisation factor is 0.32. If the overlay is
moved up to correspond to an aiming angle of 53° as shown in fig 51 more flux falls on the area and the
utilisation factor increases. The sum for one side is now 183, giving a total of 366 so the utilisation factor is
0.37.
Trigonometry
An aiming point P is selected for the
floodlight of 60° elevation. Y = 60°
O
8
60°
Z
E
20
Z + 60° = inv tan
P
F
20
( 8 ) = 68°
Z = 8°
O
X
B
E=
17500 × 0.37 × 0.8
= 13 lux
400
E
10
X = inv tan
8
Using the utilisation factor of 0.37 to find the average
illuminance over the area:
N × F × UF × MF
E=
A
where:
E is the average maintained illuminance
N is the number of luminaires, in this example 1
F the initial lamp lumens, 17500 lm for a 150W high light
output HPS lamp
UF the utilisation factor, 0.37
MF the maintenance factor, for this example assumed to be
0.8
A the area illuminated, 20 × 20 m
10
( 8 ) = 51°
8
E
O
68°
W
400
20
F
10
A
15+11=26
28+26+3=57
17+14+4=35
10+8+4=22
8+7+5+1=21
Total=161
20
20
= sin 68° OF =
= 21.6
OF
sin 68°
(
10
W = inv tan 21.6
) = 25°
W = 25° X = 51° Y = 60° Z = 8°
Fig 49 Trigonometry of lit area
Fig 50 Areaflood 15 with overlay for aiming angle at 60°
24
Floodlighting
Illuminance at a point
To examine the uniformity of a proposed
floodlighting scheme requires illuminances
to be calculated at specific points. The
inverse square and cosine laws of
illumination explained in the Lighting
Theory module can be used for this purpose.
29+22+1=52
28+27+5=60
17+14+6=37
10+8+5=23
4+3+3+1=11
Total=183
The formula for the illuminance on a surface
due to a relatively small light source is:
I× cosA
E = d2
where:
I is the luminous intensity in cd
d is the distance between the point of
measurement and the light source
A is the angle to the normal to the surface on
which the light is falling
In floodlighting the effective source intensity
is the photometric value multiplied by the
maintenance factor. Values of luminous
intensity can be read from the floodlighting
Fig 51 Areaflood 15 with overlay for aiming angle at 53°
data, either from the intensity curve or the
isocandela and zonal flux diagram. The intensity curve can be used to read off intensity values in the
horizontal and vertical planes in angles relative to the peak intensity in the vertical plane. (See also p19 and
fig 40) For angles that do not lie on the horizontal or vertical plane the isocandela diagram can be used. In
all such calculations it is always worth drawing a clear diagram to identify the angles being sure that they
are expressed as vertical and horizontal angles relative to the floodlight in question. For both diagrams the
intensities are given in cd/1000 lm so it is just a matter of multiplying by the lamp lumens divided by 1000
to give the actual intensity in candelas.
The use of the isocandela diagram can be illustrated by calculating the illuminance at one corner of the
20m x 20m area examined previously (Fig 47). This is could be the minimum illuminance, and so the ratio
of the average 13lux to this value is one uniformity measure that is likely to need checking. The
illuminance expression:
I × cosA
I × cos3A
E=
can
be
rewritten
E
=
where H is the mounting height of the floodlight.
2
d
H2
The angle A is between the column EO and the line OA. CosA can be expressed as cosW × cos(Y+Z) by
using trigonometry, giving in this example cosA as 0.34. Reading the isocandela diagram (fig 48) it is
estimated that the intensity is 400 cd/1000lm. With a maintenance factor of 0.8, initial lamp lumens of
17500lm, and one Areaflood 15 on the column, the illuminance at the corner is given by:
E=
17.5 × 400 × 0.343 × 0.8
= 3 lux
82
3
The uniformity, of minimum to average illuminance is therefore, 13 about 0.23.
Lighting design software
For the many of floodlighting problems the use of a computer with lighting design software
is unnecessary, but on the more complex projects where many repetitive calculations must be carried out
to find the uniformity of illuminance on the horizontal, vertical, or inclined planes it can be valuable.
However, the computer can only act as a design aid in the limited sense that the final printout of the
results can tell the designer quickly and accurately whether the design works or not.
25
Floodlighting
It is usual in these cases to define an XY grid covering the area. The steps in X and Y can be selected to
give either a coarse or fine grid, depending on the requirements. The positions of the floodlights are then
defined in terms of X, Y, Z for altitude. Floodlight aiming can be noted either in degrees of elevation and
azimuth or by using the X and Y co-ordinates of the point at which the peak intensity reaches the area.
The photometric performance of the floodlights is then accessed in the form of an angular grid. The
intensity values between grid points are handled in the lighting design program either by curve fitting or
by straight-line interpolation. Floodlights with fast rates of change in their intensity distribution (i.e.
precision floodlights) need to be photmetered very accurately and require considerable data to be used if
the result is to be reliable. It is also necessary to define the format for printout presentation. This can be
tabulated in the form of a chosen grid, or isolux diagrams. By using standard lighting formulae in the
program the printout can be in terms of horizontal, vertical, inclined-plane, mean cylindrical, or any other
form of illuminance for the whole or part of the specified grid.
The new version of Thorn's TL Vision will include the ability to do lighting designs for outdoor and
indoor lighting supported by a comprehensive database of photometric data for outdoor and indoor
products. There is to be the capability of doing street and amenity lighting designs. Also included with the
software there will be an electronic catalogue.
The Thorn Lighting Optilume Flood lighting design software is capable of handling simple and fairly
complex floodlighting designs. Optilume Flood is a lighting design program that operates in DOS that is
dedicated to the design of outdoor lighting schemes. The program considers two classes of design:
• Area lighting. The designer specifies the area and luminaire positions. From this the program
calculates, displays and provides a printout of the horizontal maintained illuminance over a grid of the
area, including a summary of the minimum, average and maximum illuminance with the uniformity and
diversity. At each point covered by the horizontal grid, the vertical illuminance for a selected direction and
height can be calculated, including a summary of the minimum, average and maximum illuminance with
the uniformity and diversity. The average overspill illuminance for a selected direction and distance can
also he calculated. This is useful for establishing the degree of light spill or light pollution to the
neighbourhood. For the lighting of sport arenas, an option to display a sport layout is included.
• Building lighting. The designer specifies the
building size, surrounding area and luminaire
positions. From this the maintained illuminance over
a grid on a building face is calculated, including a
summary of the minimum, average and maximum
illuminances, with the uniformity and diversity.
Optilume flood includes a scheme file management
system, so that the user has control of the design
scheme files that are stored, erased and copied.
24 m
8m
16 m
An example scheme has been carried out with the
layout in fig 52. This arrangement, using three 150W
Areafloods (AF15S150W.4) on 8m columns, is an
area that is three times the mounting height wide and
the floodlights are spaced twice the mounting height
apart. The aiming angle is 63° corresponding to
aiming 2/3 across the width. (This is similar to the
example given with the zonal flux diagram.) The
horizontal illuminance results are:
48 m
16 m
8m
Y
(0,0)
Fig 52 Layout for example scheme
26
X
Floodlighting
Minimum
4 lux
Maximum
25 lux
Average
14.5 lux
Min/Max
0.15
Min/Avg
0.26
On the basis of initial lamp lumens of 17500lm and a maintenance factor of 0.8.
A part of the luxplot is shown in fig 53 and the shading diagram is shown in fig 54.
Fig 53 Part of Luxplot of sample scheme using Optlilume Flood
Fig 54 Shading diagram of sample scheme using Optlilume Flood
27
Floodlighting
It is an advantage for lighting design programs to be able to calculate
the average overspill illuminance for a selected direction and distance.
As this is useful for establishing the degree of light spill or light
pollution to the neighbourhood. In the Outdoor and Amenity
Lighting module section 2 covers Avoiding Light Pollution and can
be referred to for this topic. It includes details on the Institution of
Lighting Engineers ‘Guidance Notes for the Reduction of Light
Pollution’.
Fig 55 In rural areas lighting
should not be intrusive.
Questions 2
1.
Name four different ways of presenting photometric data for a floodlight.
2.
What type of light distribution is given by the Areaflood 40 whose beam data is shown in fig 38?
3.
Use fig 41, the isolux diagram for the AFSS250.T mounted at 8m to calculate the initial illuminance at
a grid position of (12m,12m) when the mounting height is 12m. Take the initial lumens of the lamp to
be 27500lm.
4.
If an open area with obstructions is to be lit by floodlights from opposite sides, what maximum spacing
in relation to the mounting height would you recommend between opposite columns and columns
next to each other on a perimeter.
5.
Using the data in fig 48, and initial lamp lumens, determine the amount of flux in lumens that is
beyond the beam.
6.
In fig 47 what is the angle POG?
7.
Find the illuminance at the point B shown in fig 47 using the isocandela diagram in fig 50. In the
calculation use a maintenance factor of 0.8.
8.
For the layout shown in fig 52 what approximate average illuminance is given by the Thorn
Floodlighting Calculator?
28
Floodlighting
4
Floodlighting applications
Industrial
Many industries use production processes or have fabrication and storage requirements that necessarily
have to be totally in open space. Typical of these are shipbuilding and repair, dockyards, ports, container
terminals, petrochemical plants, building and construction, horticulture and agriculture.
Industrial sites on urban business parks usually offer generous exterior areas and if these are not used for
work processes will most certainly be used for storage of some kind, parking of vehicles and access and will
require light after dark for these requirements as well as for night-time security.
Outdoor work and storage
Area
Maintained Illuminance
Notes
(lux)
Horizontal
10
Safety/amenity
Horizontal
20
Storage areas
Horizontal
50
Walkways and platforms
Depending on the type of work or storage, vertical illuminance may be more important. If this is so the
same values should be taken.
Outdoor industrial complexes present two common lighting problems, the multiplicity of shadows caused
by the nature of the site, and the fact that the visual tasks occur on planes other than the horizontal. The
usual approach is to design for an appropriate horizontal illuminance at ground level, assuming there are
no obstruction losses. Information of the likely or actual obstructions is needed to select the mounting
height and location of floodlighting positions to minimize shadows. The number of flood1ighting
positions should be as many as is practicable so that the illumination at any point comes from several
directions to soften any shadows that are cast. The highly obstructed areas may need additional local
lighting.
Large interior industrial areas can also be illuminated by the application of standard floodlighting
techniques. By mounting projectors at the sides of large, high buildings such as steel mills, foundries and
assembly shops, access for maintenance is made easier and illuminance on vertical planes is more easily
achieved. Such areas are often equipped with travelling cranes in which case the side mounted lighting
equipment is less likely to cause glare to workers looking upwards, and moving cranes do not cause the
obstruction which is inevitable with a conventional overhead layout of high bay reflector luminaires.
Building sites
Building sites present a special situation, in that low voltage supplies of 110 V or below are usually
mandatory for all equipment that is accessible to site workers. This means that except for large civil
engineering sites where a permanent area lighting system may be installed to cover the construction phase,
the use of high pressure discharge lighting is excluded. Thus only special linear fluorescent or tungsten
halogen luminaires can be used for temporary site lighting. Since the duration of operation is usually short
and the treatment of the luminaires tends to result in a short life, the high electrical running costs have to
be accepted.
Cargo handling, stock yards and docks
These areas are used for the storage and movement of containers and
other large stacks and objects so that the problems of light obstruction
again present a major design problem. Because most of the
obstructions are moveable, fixed local lighting luminaires cannot be
used. There will also be movements of transporter lorries, forklift
trucks and jibs or gantry cranes to be considered. Floodlights
mounted on high masts or towers, or on site buildings, can provide
Fig 56 Floodlighting of wharf
the general lighting for safe movement of rail locomotives, road
from
site building.
vehicles and personnel, with local task lighting for the handling of
29
Floodlighting
goods being achieved by projectors mounted on the crane structures. Because of vibration in these
locations, discharge lamps are generally used as they are more resilient than filament lamps, but where
stock is identified by colour coding, low pressure sodium lamps should not be used. For forklift trucks, low
voltage tungsten halogen sealed beam units offer the best solution. Additional local lighting can usually be
installed in the vicinity of fixed hoppers and conveyers.
The lighting of wharves needs to be achieved with projectors positioned some distance back from the edge
so that the working area, where loading or unloading is carried out, remains unobstructed. (Fig 56) This
arrangement may cast shadows onto the deck of moored vessels when the tide is low. Reliance will then
have to be placed on the deck lighting on board and on crane jib floodlights. Luminaires on board ship and
on the dockside must be resistant to the saline marine environment: diecast aluminium, copper, stainless
steel and suitable plastics are commonly used for this purpose. It is also important to ensure that no
dockside lighting interferes with navigational signals.
Hazardous areas
For refineries and tank farms the plant layout is extremely complex with major light obstruction and work
being carried out at various levels above ground level. High mounted floodlights, in numerous positions
sited outside the designated hazardous areas can provide lighting for
safe movement and some task work. For the many areas where
adequate illuminance cannot be provided by this system, local lighting
from luminaires will need to be installed, for example on access
ladders, walkways and at valve and gauge positions. The positioning of
these luminaires should be chosen so as to avoid glare when they are
viewed from different levels. Most of this local lighting equipment will
be bulkhead or wellglass units with high and low pressure discharge
lamps and will need to be suited to the hazard rating for the processes
and substances present in the area. Refer to section 4 'Luminaires for
Hostile and Hazardous Areas' in the Luminaires module. Some of the
information is given below.
Expert advice on the classification of areas is available from such
sources as the Authority Licensing Board or Factory Inspectorate and
the advice of the local Fire Officer can be sought. It is not the role of
lighting designers to specify zones. They are in a position to give
advice and guidance on the risk involved in installing equipment and
to answer queries on the statutory requirements that may apply.
Fig 57 Petrelux BP Grangemouth
Scotland, Petrochemical plant
The following checklist is intended to assist with
Gas
Representative Typical Application
product selection.
Group Gas
1
Zones
1
Methane
Underground mining
Zone 2 all protection concepts can be used
11A
Propane
Surface
Zone 1 all protection concepts except Ex N
11B
Ethylene
Surface
can be used
11C
Hydrogen
Surface
Zone 0 only very specialised EEx I
equipment can be used. It is more usual to
Fig 58 Gas groups
light Zone 0 areas by locating luminaires in
an adjacent area which has lower risk
Temp. Class Max. permitted
permitting the use of Zone 1 or Zone 2 products.
or T Rating
surface temp.
2
Gas Group
T1
450°C
Identify the gas that will or maybe present from the schedule
T2
300°C
(fig 58) and select a luminaire approved for this gas group.
T3
200°C
3
T Rating
T4
135°C
Use table in fig 59 to identify the required temperature class or
T rating and select a luminaire with that or higher T rating.
T5
100°C
4
IP Rating
T6
85°C
Assess the protection required against ingress by solids or
liquids to find minimum acceptable IP rating.
Fig 59 T rating
30
Floodlighting
Gas
Group
11A
T1
Acetone
Ethane
Ethyl Acetate
Ammonia
Benzol
Acetic Acid
Carbon Monoxide
Methanol
Propane
Toluene
T2
Ethyl Alcohol
I-Amyl Acetate
N Hexane
N Butane
N-Butyl Alcohol
11B
Town Gas
Ethylene
11C
Hydrogen
Temperature Class
T3
T4
Petrol
Acet Aldehyde
Diesel
Ethyl Ether
Aviation Fuel
Heating Oil
T5
T6
Carbon Disulphide
Fig 60 Schedule of common gas groups and T rating
Select a luminaire with IP rating with both digits not less
than the required number.
Equipment used in hazardous industrial areas is approved by
BASEEFA (The British Approvals Service for Electrical Equipment in
Flammable Atmospheres). Luminaires are tested to the appropriate
British Standard and, on compliance BASEEFA issues a Certificate of
Assurance that is valid for three years and needs to be renewed after
then. The certificate is essentially concerned with hazardous area
protection and does not apply to IP rating or corrosion resistance.
Luminaires for use in coal mining and explosives processing are
submitted for type testing by SMRE (The Safety in Mines Research
Fig 61 Petrelux Arrowhead
Establishment).
Drilling Rig
Quarries
Quarries and open cast mines present a situation where the dimensions change, both the extent and depth
of the area will increase as work progresses. As the floodlighting installation will probably be permanent,
the design should be based on the ultimate size of the excavations where this can be established. As the
distances increase, so additional luminaires will be installed, or brought into operation, and some reaiming may be necessary. Due to the dirty nature of these sites, adequate allowances for maintenance and
atmospheric losses should be included in the design
calculations.
Some Basic Principles
Security lighting
The applications described so far have been working areas
without access by the general public. Security lighting
provides a link with the following section dealing with
commercial areas. The security of property and people is
equally important in both application areas. The prime
objectives of security lighting are to deter criminal activity
or, if that fails, to detect and prevent it. For private premises,
the lighting should enable intruders to be detected. For
public areas, the lighting provides general amenity to give a
feeling of safety and well being while enabling security staff
to monitor potential or actual criminal activity.
Detection may be directly visual or indirectly by a closedcircuit television (CCTV) system. In either case vertical
31
Reveal intruder - Light to give clear
observation of intruders. They will show
up in silhouette against bright
backgrounds such as floodlit walls.
Deter intruder - Glare is often
deliberately directed outwards towards
the perimeter, so that an intruder will
face the discomfort and confusion of
'bright' lights.
Conceal defender - An intruder exposed
to glare will not know if there is a
defender behind the lights and the guard
can observe without being seen. The
intruder may be deterred from the crime.
Floodlighting
illuminance is the most relevant design criterion. The aim is
often to reveal intruders so that facial features and build can
be seen well. In private areas the illuminance does not need to
be very high since the human and electronic system can
operate in low ambient conditions and the degree of detail to
be detected is quite coarse. This is not the case in public areas
as the illuminance required for amenity is higher and also a
greater quantity and quality of lighting is justified to ensure
that good quality video recordings can be made to aid in the
identification of suspects. The designer will need to obtain,
from the camera manufacturers, information on the
illuminance, and colour properties necessary to achieve the
required picture quality.
Fig 62 Perimeter lighting terms
One purpose of security lighting is to deter crime and
vandalism. A possible exception to this is in the case of
military or other sensitive sites. It can be argued that the
lighting draws attention to the existence of the premises. It is
therefore possible to adopt ‘discreet’ infrared systems where,
to the intruder, the site appears to be in total darkness while
the guards can observe occurrences via infrared television
cameras. The rest of this section will deal with the more usual
visible lighting systems.
A distinction can be drawn between the lighting of
Fig 63 Double perimeter fence
unattended and attended sites. Unattended sites are subject to
surveillance by police or security guards from outside the premises and the lighting merely allows for the
detection of unauthorised movement. Such lighting is directed inwards using high-efficiency, long-life
luminaires mounted as high as possible to obtain maximum coverage and to minimise interference or
mechanical damage. On an attended site, usually with a gatehouse at the entrance, floodlights should be
directed outwards so that the whole field of view from within the building, either directly or by closedcircuit television, is adequately illuminated. The whole aim of such an installation is to subject potential
intruders to maximum glare so that they feel vulnerable and do not know if their presence has been
detected or not. The disadvantage of such a system, particularly in residential areas, is light trespass into
adjacent property and the problems associated with obtrusive light.
An alternative approach to having a security lighting system operating throughout the night is to have it
linked to an alarm system which, when activated, switches the lighting instantaneously so that a visual
assessment of the situation can be made. In this case only tungsten halogen lamps can be used, but as the
hours of use are very short the increased energy load is acceptable.
Security lighting techniques must be tailored to local conditions: the landscape, the architecture, the
layout of the buildings and roads, the adjacent premises and the length and nature of the boundary and its
walls or fences. There are five basic lighting techniques, which can be adapted to suit almost any situation:
• Perimeter lighting
• Checkpoint lighting
• Area lighting
• Floodlighting
• Topping up
Perimeter lighting - The land about some premises is enclosed by solid walls or fences, the most common
and effective arrangement is for land to be surrounded with chain-link fencing. This fence permits security
staff to see out and they let light from the security lighting to fall on the surrounding land, both these
factors making surreptitious approach difficult. The terms used to describe the features of the fencing and
lighting at the perimeter are shown in fig 62.
Fence zone: a strip of land 4m wide, centred about the line of the fence. This is the zone in which crime
may take place if not prevented by lighting and supervision.
32
Floodlighting
Sterile strip: also known as the no-man's-land, this is the
area inside the fence which is lit and which the intruder has to
cross. This strip and the fence zone should be completely
clear of all obstructions. Preferably it will be weed-free or will
be paved or covered with gravel. Detection devices here may
be buried in the ground.
Stand-off distance back (d): distance between the array of
luminaries on columns and the fence line.
Spacing (s): distance between luminaires (or clusters of
luminaires) on columns.
+
Mounting height (h): distance from the light-centre to the
ground.
Fig 64 Section through checkpoint hut
Surveyed field (f): distance outside fence at which
movement must be detected.
If a double fence is used, the luminaires may be mounted on
columns immediately behind the inner fence (Fig 63). The
spacing between fences is usually not less than 6m to make
bridging difficult.
Checkpoint lighting - A strong perimeter does much to
diminish the risk of crime, but can increase the chance that a
Fig 65 Control barrier without gate
determined criminal will attempt to enter or take out stolen
goods via a normal gate. This may be done by trick or force. Thus it is necessary to design gatehouse
lighting so that the tactical advantage is with the guards. Good checkpoint security lighting will enable
people, vehicles, goods and documents to be checked thoroughly. The lighting in the gatehouse should be
shielded and subdued, (dimmers can be used), to prevent reflections in the windows, which could interfere
with a clear view of the exterior. This prevents the gateman being seen from outside the site, it ensures
that his own view out is not hampered by bright reflections from the inside of the windows and that his
own dark-adaptation is maintained. (Fig 64)
At the checkpoint, it is a convenient arrangement to have local floodlights to light into trucks or vans with
sufficient light to enable a proper search (Fig 66, A). A luminaire located on or under the canopy (B) may
be necessary to give a good light for seeing into driving cabs for checking occupants and papers. The zone
in front of a check-bar should be well lit so that the vehicle can be inspected in detail. The road can be
painted white so that light is reflected under the vehicle to aid searching. Alternately, robust recessed
luminaires, like Mica can be recessed into the road surface for the same purpose (C). It is a good idea to
place a light-coloured wall or a chain-link fence (D) along the blind side of the vehicle to prevent goods or
persons getting pass the guard.
A perimeter fence can be returned along the line of an entrance roadway, and the space between the two
facing fences brightly illuminated. (Fig 65) This creates a 'funnel' through which it is near impossible to
pass unseen, often sufficient to deter the entry of unauthorised persons, even if there is no gate.
C
Fig 66 Checkpoint lighting
33
Floodlighting
Area lighting - This technique of illuminating an open space
employs methods similar to those used for lighting outdoor
work and storage spaces. The luminaires can be mounted on
adjacent buildings or on columns along one or more sides of
the areas. There may be a small number of lighting towers,
carrying a number of floodlights, positioned at the corners of
the area. Another method of lighting is the 'high mast
technique', where a small number of masts about 30m high
are positioned to light a very large area.
Fig 67 Floodlighting for security
Floodlighting - Floodlighting a building or a wall creates a
bright background against which an intruder may be readily seen. (Fig 67) If the district brightness is low,
the thief, standing in the space between the building and the floodlights finds himself in a dilemma. Going
forwards towards the building will increase the likelihood of his being seen, yet to retreat towards the
floodlights is dangerous for him as there may be policemen or security guards behind the glare of the
lights. In fig 67 if the intruder is in zone A he will be clearly revealed by the direct illumination of the
floodlights. If he is in zone B he will be seen in silhouette against the luminance of the building. Properly
used in conjunction with wire fences, floodlighting can give a unique strategic control of security.
Topping up - Topping-up luminaries form part of the plan to ensure that there is not a single place around
or within the defended area where an intruder can hide, nowhere for a vehicle to be parked out of sight
and nowhere for goods to be left for an accomplice to pick up at another time.
Several of these security lighting techniques can be used for prisons and detention centres. Here security is
concerned with preventing inmates leaving and making it difficult for accomplices outside to assist in any
escape. Floodlighting of the boundary area is the prime requirement. In the case of a double chain link
fence, the space between the fences should be lit with floodlights, or road lighting luminaires, mounted
inside the inner fence. Where sufficient land is available, this idea of a security ‘corridor’ can also be used
to protect private premises. In the case of a high prison wall, the area
immediately inside the wall, and the outside if it is patrolled or
covered by CCTV. The perimeter wall is commonly lit by groups of
floodlights mounted on the wall.
Commercial
There are many large interior commercial areas, such as covered
malls and atria where floodlighting techniques are often used. (Fig 68)
In these situations besides the visual and lighting requirements to be
met there can be light requirements associated with the growth of
trees and plants. In indoor swimming pools floodlighting is frequently
used. Here attention needs to be given to considerations of glare,
direct and reflected from the water, as well as the ability of the
Fig 68 Channel Tunnel
floodlights to withstand the thermal and atmospheric conditions of
Folkestone
transport terminal
the space. (Fig 69)
The aim of commercial floodlighting is to provide amenity in public
areas and create an attractive night-time visual environment rather
than providing for exacting visual tasks to be performed. The lighting
of vehicle parks may be fairly functional and utilitarian but the
majority of the applications described in this section are aimed at
promoting sales, leisure or tourist activities or at expressing civic pride
or corporate status.
Sales areas
The floodlighting of exterior sales areas such as petrol filling stations,
used car lots, garden centres, etc. serves two main functions: to
advertise their presence, and to enable customers to examine and
purchase the goods. In the first case, the illuminance will depend on
34
Fig 69 Mill House Leisure
Centre swimming pool
Floodlighting
the district brightness and a high proportion of vertical plane illuminance is required. Secondly the
directional and colour qualities of the lighting should complement the goods being displayed. Where
money changes hands under the floodlighting, rather than in a separately illuminated kiosk, the colour
rendering of high pressure sodium lighting can cause problems of differentiating between copper and
silver coins. Low pressure sodium lighting is unacceptable for all sales areas.
As these premises are usually sited on main roads, the floodlights should be aimed to avoid glare to passing
motorists and pedestrians. For petrol stations, the installation must also meet the requirements of the local
petroleum officer.
Car parks
Set out below is the current illuminance recommendations for car
parks. These clear up some previous disparities between CIBSE and
BS recommendations. Since average and minimum illuminance values
are given calculation methods should be adopted to establish that the
criteria are met. Zonal flux diagrams can be used to estimate the
utilisation factor, UF, and point illuminance. Alternatively, a design
aid such as the Thorn Optiliume Flood software could be used. The
Thorn Floodlight Calculator can be used for preliminary designs.
During the design it should be remembered that vertical illuminance
is important to reduce the fear of crime and to see facial expressions
easily.
A simple way to determine a preliminary layout of wide angle
floodlights around the perimeter of an area is to work on lighting a
Fig 70 Car park floodlighting
depth of the area equal to three times the mounting height, and that
the lateral spacing between floodlights is about three times the mounting height. The chosen height will
often have to be a compromise. It needs to be high enough to ensure that floodlights are well above parked
vehicles, which throw increasing lengths of shadow with increasing distance from the floodlight positions,
and to minimise glare to drivers using the car park. At the same time the height must be related sensibly to
the height of nearby buildings, it may well be limited by Local Authority bye-laws. If the method given
above for determining the layout of equipment indicates that pole heights are going to be excessive, the
alternative is to use post-top luminaires having a symmetrical light distribution on shorter columns
arranged in a regular array at a spacing to height ratio of 3 or 4. Column height may vary between 3m and
12m. Height should be kept in scale with surroundings.
Outdoor Car Parks and Multi-storey Roof Level Car Parks (BS5489: Part 9, 1996 Recommendations)
These replace the recommendations in CIBSE LG6 The Outdoor Environment Lighting Guide
Area
Average Illuminance (lux) Minimum Illuminance (lux)
5
15
Rural, Zone E1 and E2
10
30
Urban, Zones E3 and E4
10
30
Multi-storey roof level (Use Zone E1)
• Average illuminance is maintained horizontal at floor level.
• Minimum illuminance is maintained horizontal at floor level at any point within the calculation grid,
which should be no more than 1.0m from the wall or perimeter of the area.
• When the minimum uniformity (min./ave.) is less than 0.33 the average illuminance will need to be
increased accordingly.
35
Floodlighting
Lorry parks
Lorry parks are most satisfactorily lit from the perimeter of the area to reduce the risk of damage to poles
and floodlights caused by vehicles. If this is not practical, crash barriers should enclose island-sited
columns. The inherent height and bulk of lorries require that perimeter floodlights should be mounted at
least 12m from the ground to ensure some reduction of shadowing, which will be far greater than in a car
park. At these heights the number of columns can be minimised, each supporting a number of
floodlights, if necessary trained in different directions. Where island-sited positions are used, it is usual to
mount floodlights on freestanding single columns at heights of 30m or more. Such columns are usually
fitted with headframes that can be lowered for maintenance of the luminaires, or are the hinged column
type.
Lorry Parks
Area
Low risk - normal parking
High risk - normal parking
Loading and unloading
Average Illuminance (lux)
20
30
50
Sign lighting
The quantity of light required from floodlights to illuminate signs will depend on the:
• size of the sign,
• distance from which it is viewed,
• contrasts of various parts of the sign with each other,
• and the ambient lighting conditions.
A small sign, or one to be viewed from a distance, will need more light than will a large one or one to be
read at close quarters, if it is to be readily noticed. When the sign message has the maximum contrast with
its background, the amount of light required is a minimum. A sign in a city centre where there is a high
ambient illuminance from shop windows, streetlights, and other nearby illuminated signs will require a
substantially higher luminance than will the same sign in a suburban area. The illuminance ranges
for advertising signs below gives general guidance, but should be used with discretion. Most signs are
viewed from below, so floodlights for externally lit signs should be mounted on brackets from the top of
the sign rather than from the bottom, to prevent obstruction. Alternatively, on some sites the
floodlights could be mounted on the ground. Many signs have a specular surface, so floodlight locations
must be chosen so that direct reflections of the illuminating sources do not prevent the sign being read.
Also, since it is rarely possible for the light from generally available commercial floodlights to be confined
to the sign, care should be taken to ensure that spill light beyond the sign does not cause annoyance. To
allow for variations in light distributions from one floodlight to another it is advantageous to provide
for directional adjustment in the fixing arrangements. To obtain a reasonable uniformity of illuminance
along the length of a sign, luminaires bracketed from above should be spaced laterally at between 2.5 and 3
times the bracket length, provided that asymmetric wide angle floodlights are used. If units are overspaced, a scalloping effect will be created. The bracket
length should be no less than one-quarter of the sign height.
S must not exceed 2.5 × D
D must not be less than 0.25 × H
Under these conditions, a very approximate method of
calculating the illuminance on a floodlit sign is to take onethird of the total luminous flux of all the lamps and divide this
by the area of the sign in square metres to give
the illuminance in lux.
H
UK Local Authorities frequently have byelaws covering the
luminance of advertising signs to ensure they do not cause
glare. It is therefore advisable to obtain clearance from the
Local Authority for a proposed sign before proceeding.
D
S
Fig 71 Lighting an advertising hoarding
36
Floodlighting
Signs
Recommended maximum luminance for illuminated signs (Draft ILE document publication Oct 2000)
Illuminated
area (m2)
Up to 1
1 - 10
over 10
Curfew
Before
After
Before
After
Before
After
Zone E1
50
0
-
Zone E2
Zone E3
Zone E4
400
400
800
800
1000
1000
400
800
1000
300
600
600
Note: An illuminance of 1000 lux and reflectance of 80% corresponds to about 250 cd/m2
Buildings
When it comes to lighting building facades the complete facade
should be illuminated to some extent in order to show the entire
building outline to the viewer. This maintains the proportions of the
architecture and allows the more prominent and desirable features to
be given emphasis. If possible a building needs to look more than just
an illuminated front. Its solidity can be emphasised by adding light at
a lower illuminance to the side, or at the very least to the return
corners, allowing the illuminance to decay gradually to the rear of the
end wall. It may be necessary to illuminate a sloping roof to achieve a
coherent picture, otherwise chimney stacks may appear as if they are
suspended in mid-air.
It may be desirable in some cases to soften the strong modelling effect Fig 72 Light revealing features in
of uni-directional light. This may be achieved by illumination in the
the architecture.
form of fill-in light from a completely opposite direction to the main
flow of light. Any fill-in light should be only one tenth the value of the main illuminance.
There are broadly four basis architectural styles for building facades:
• Facades that are basically flat
• Facades with predominantly vertical characteristics
• Facades with predominantly horizontal characteristics
• Facades with external recesses
Facades that are basically flat
For example undecorated fronts of factory units and spec-built office
blocks. The achievement of any shadow effects may only be possible
by placing the luminaires at exceptionally close-offset positions,
unless for security surveillance a high level of uniformity is required, a
certain unevenness in the brightness patterns across the facade could
produce a degree of visual interest.
Fig 73 Flat facade.
37
Floodlighting
Facades with predominantly vertical characteristics
This is characteristic of both medieval and classic architecture. The
style can be emphasised by applying illumination from the left and
right side of the facade using medium beam floodlights. Generally,
due to fairly light coloured surface material, the shadow formed by
sharply oblique lighting are too strong and create too distinct a
contrast. In-fill lighting from the opposite direction using wide-beam
floodlights will reduce the contrast and soften the appearance.
Facades with predominantly horizontal characteristics
A great many modern high office and hotel blocks have a markedly
horizontal emphasis. Often such designs include horizontal elements
that project slightly, like window ledges or continuous bands that run
across the facade from one side of the building to the other.
Floodlights placed close to the facade and aimed upward will produce
bands of dark shadow above the projection. The wider the shadow
band the more likely it will be that the surface area of the facade above
the projecting ledge will appear to be floating on air and the building
will appear as dismembered sections. Supplementary lighting may be
placed upon the ledge to soften or eliminate the shadow, or
alternatively, the floodlights have to be moved away from a closeoffset position so that a greater distance exists between the facade and
the light source.
Fig 74 Vertical facade.
Fig 75 Horizontal facade.
Facades with external recesses
A facade is often designed to incorporate features such as balconies or
galleries that may project forward or be recessed into the facade. In
both cases the floodlights must be located some distance in front of
the building in order to prevent excessively dark shadows being
formed.
If lack of available space in front of the facade prevents this,
supplementary illumination will have to be placed inside the balcony
space or incorporated within the object creating the shadow as in
fig 76. A technique that can be considered is to place small exterior
low voltage tungsten halogen luminaires on ledges of the facade whilst
hiding the transformer for the lamp within the building at close
quarters.
Fig 76 Facade with recesses.
Guidance on illuminance
To ensure that a floodlit building stands out from the surrounding area, its luminance must be raised in
relation to the district brightness, but there are other factors that influence the visual impact achieved. A
small isolated surface will require a higher luminance than a large building in the same surroundings, while
for similar size and luminous environment, an object seen from a distance will need a higher luminance
than one viewed from nearby. Based on the various recommendations that exist, the following ranges of
average luminance can be considered:
•
•
•
rural sites with little or no road lighting and competition from other illuminated buildings and
signs - up to 5 cd/m2,
towns and suburban areas with medium district brightness - 5 to 10 cd/m2,
city centres and other brightly lit areas - 10 to 15 cd/m2.
To arrive at the average maintained illuminance to achieve the luminance target, the diffuse reflectance of
the building surface and its state of cleanliness must be known. The colour of the light source and the
building surface will also affect the result.
38
Floodlighting
Using near white light sources and assuming the reflectance of the
surface is diffuse the design maintained illuminance is given by the
formula
Em =
where:
Em
Ls
MF
R
π × Ls × MF
R
Average maintained illuminance
Luminance of surface
Maintenance factor
Average reflectance
Highly specular, smooth surfaces, such as glass, gold leaf, aluminium,
stainless steel, mosaic, glazed brick and tiles, can present particular
Fig 77 Match luminance to
difficulties when floodlighting buildings. In daylight, with the main
district brightness
source of light from above the building, specular reflections are
projected downwards towards an observer and these materials appear to sparkle and shine and, in the case
of heat reflecting glass, reflect a clear image of the sky and clouds. When floodlights are installed at
ground level, the direction of the light is reversed and any specular reflections are directed skywards. To
the observer these building materials will look dull compared with their daytime appearance.
Building lit appearance
The best installations are those that exploit the differences between
day and night rather than attempting to minimize them. It might be
argued that buildings should be floodlit from the top. However the
appearance of the floodlights and long brackets is unsightly during the
day and most surfaces have a specular component that produces high
luminance images of the lamps at the top of the walls when viewed
from below.
A coherent flow of light across a facade is desirable, implying one
general aiming direction for the main floodlights. (Fig 78) This should
not coincide with the most common viewing direction for the
building, since no shadows will be visible and the building will appear
flat. The main floodlighting should come from a substantially
Fig 78 Provide a coherent flow of
different angle.
light across a facade
Completeness of floodlighting is important in that the whole building
and its setting should be revealed, This may include the return walls
to the main facade, the roof and the full height of any projection from
the roof such as chimneys or adjacent walls, trees or shrubbery. The
main floodlights usually need supplementing to give completeness and
avoid a ‘floating’ appearance. Buildings can appear to float if the base
of the building is shadowed or underlit. In urban areas where
buildings usually rise direct from the pavement, floodlighting of the
ground floor facade is near impossible, but in this situation the road
lighting can usually be relied upon to prevent the building ‘floating’.
Wherever possible, luminaries should be hidden from view by being
installed behind existing structures or purpose-built features. With
Fig 79 Floodlights co-ordinated
close offset floodlighting, where the projectors can only be mounted
with architectural features
on ledges, cornices and balconies, they should be spaced so that they
coincide with architectural features of the facade such as window recesses or columns between the
windows. (Fig 79) Some scalloping between the floodlight will be inevitable but this can be acceptable so
long as the shadow pattern relates to the form of the facade. With close offset mounting projections higher
up on the facade long shadows will be cast, requiring the installation of equipment at several levels on a
high building. This technique requires floodlights with a narrow transverse and wide axial beam with good
spill light control. It may also be necessary to use screens to prevent very high luminance patches on the
surface immediately in front of the floodlight. Close offset lighting has the advantage for occupied
39
Floodlighting
buildings, such as offices and hotels, that there is very little light
penetration into the building to cause annoyance or discomfort to the
occupants.
Coloured light can be used to produce a deliberately festive
atmosphere or, with more subtlety, to emphasize the form and depth
of a structure. For subtle effects lamps of differing colour
temperatures can be used rather than resorting to the use of colour
filters.
Calculation techniques and photometric characteristic of floodlights
do have relevant to building floodlighting. However the direct
experience of taking a floodlight outside at night, point it at
something, walk round, look at the varying patterns of light and shade
is invaluable.
Fig 80 A warm colour to give
attractiveness to a public house
Sports
There is only one floodlighting application where the values of recommended illuminance are commonly
greater than those required for interiors. This is in the lighting of large areas for spectator sports. It is
worth noting that many interior sport areas also use floodlighting techniques. In a stadium, spectators may
need to see relatively small detail and fast movement at distances of 150m or more. To achieve this, the
illuminance will need to be higher than that strictly dictated by the visual needs of the players. Where
sports are televised, the demands of the camera system may dictate an even higher illuminance that is in
excess of the minimum visual needs of the spectator.
Televised and spectator sports apart, many sports can be played at lighting levels comparable with, or even
less than, those provided in commercial or industrial interiors. The level to be recommended depends on
the size and speed of the critical object, which obviously vary from sport to sport, and on the standard of
play or competition. In accordance with the standards set by international sporting authorities, the CIBSE
Lighting Guide No. 4 (1999) recognizes up to six categories of play:
• recreational
• supervised training and practice
• club
• county
• national
• international
This does not necessarily mean that there are six distinct illuminance
values for every sport as the individual governing bodies sometimes
group these categories in different ways. Adherence to the
recommendations results in the players and officials finding comparable lighting conditions for both 'home’ and ‘away’ fixtures.
Fig 81 Parc des Princes, Paris
with PRT 2000 floodlights
There are a number of sports, for example tennis, soccer, rugby and
baseball that are played on areas for which the dimensions are closely
specified. This allows for lighting with standard pole and floodlight
layouts to be recommended. Floodlights are often aimed at rightangles to the main direction of play, with the poles sited sufficiently
far back from the sides of the area to ensure that players will not
collide with them and to ensure that the near sidelines are adequately
lit.
For economic reasons the number of poles is kept to a minimum,
commensurate with providing reasonable uniformity, which
frequently means large lumen packages at each position. This
increases the possibility of glare in viewing directions towards these
groups, so floodlights are mounted usually as high as is practicable.
40
Fig 82 Recreational hockey
Floodlighting
+
+
+
223
243
240
253
218
258
249
279
266
270
266
302
252
308
263
237
321
285
246
310
262
237
321
286
232
286
265
270
267
302
207
243
239
254
219
258
+
+
+
Average illuminance 270 lux Uniformity 0.77
Fig 83 Chingford Tennis Club
Floodlighting of tennis courts
imposes a number of demands,
especially on smaller clubs. The
cost of the 10m high columns
recommended under the current
Codes of Practice can be
prohibitive while planning
permission can add further
Fig 84 Tennis court lighting at 6m mounting height with six 250W
difficulties. Once installed, the
low glare Sonpak floodlights (OTLGB250.4)
lighting can produce
unacceptable glare for players and stray light may annoy neighbours. A solution has been evolved using a
low glare version of the well-established Sonpak 250W high pressure sodium floodlight mounted on 6m
columns. The system controls glare and spill light whilst meeting the average illuminance requirements
for club play of 260 lux. (Fig 83 & 84)
Television
For spectator sports in large stadia where television coverage is
required, illuminance related to the camera takes priority. For most
sporting events there are seldom less than three fixed cameras and this
number is often supplemented by other fixed or mobile cameras. For
games such as soccer, rugby and ice-hockey (except for special
incident and action replay shots), cameras are limited to one side of
the arena and behind the goals, so that cutting between cameras does
not produce an apparent change in the direction of play for the
television viewer. For athletics, cricket and baseball, cameras are
placed around the complete area.
Fig 85 Stadium using 2kW metal
The lighting criterion for television has previously been based on
halide Mundial floodlight
illuminance in a plane normal to the 'main' camera position but, in
view of the increasing number of cameras being used, the specification
now applies to four vertical planes at each measurement point.
(Fig 86) The average maintained illuminance in each of these planes
over the field of play is typically between 500 and 1400 lux. This
depends on the type of sport, particularly in respect of the speed of the
action occurring during camera shots and the 'camera shooting
distance’, over a range from 25 to 150m. Diversity limits for
illuminance in the vertical and horizontal planes are given in Fig 3.
Meeting the specifications for both the average value and the variation
Fig 86 Illuminance measurements
will ensure that adequate picture quality is achieved at any camera
position, based on a signal/noise ratio of 50 dB.
at each grid point
41
Floodlighting
In the case of outdoor installations, or indoors where there is a
significant daylight contribution, the colour temperature of the
floodlighting must be between 4000 and 6500K where the lighting is
used during the day and into the evening. This is to minimize
apparent colour changes in the scene when daylight is progressively
replaced by the floodlighting.
Other applications
Lighting near airports
Part 8 of BS5489 Road Lighting gives recommendations for lighting
within defined areas around aerodromes, railways, harbours and
navigable waterways, additional to the general recommendations of
other parts of BS5489.
Fig 87 Manchester Indoor Arena
In particular when planning lighting installations near aerodrome it is
essential to consult the appropriate authorities, including the Planning Authority and, in the case of
military aerodromes, the Aerodrome Senior Air Traffic Controller and for civil sites, the Civil Aviation
Authority. 'Near' is taken to be 3 miles or 4.8 km.
There is a specification for limiting the light distribution for luminaires in the vicinity of aerodromes.
Angle from downward vertical
90
92
94
96
100
110
120 and above
Maximum permissible intensity
(cd)
750
300
95
75
60
40
30
The requirement to limit light above the horizontal necessarily favours the use of flat glass lanterns and
floodlights.
Currently there is a revision in preparation to replace the current part 8 of BS5489.
Solar simulator
This is an unusual application. Floodlights are used to create an 'artificial sun', to mimic the luminous
intensity and power of the sun over a small area. Basically a frame carrying a battery of 36 x 1kW CSI
floodlights, with the control gear mounted in a cupboard at its base can be directed onto components that
are under test. They can be subjected to a luminous output of
1000W/m2 and a uniformity better than 0.85. Typical applications
have been the testing of solar panels and various materials used in the
aircraft industry, for example the nose cones of new jet fighters.
Planning permission
In general terms planning permission will be required for all exterior
floodlighting schemes. It is therefore wise at the initial stages of considering floodlighting to determine ‘in principle’ if planning consent
will be granted for the proposed floodlighting. This can save
considerable abortive work. This initial consent is described as outline
planning permission and simply confirms that the local council is
prepared to consider the installation of floodlighting in that particular
area.
42
Fig 88 Solar simulator
Floodlighting
The outline planning application should contain all relevant details
regarding the location of the area, ideally as it is shown on an
Ordinance Survey map sheet. A brief explanation on the usage of the
area, together with a list of measures that will be taken to minimise
the nuisance to adjoining residential properties can be helpful, along
with a general description on the proposed type of floodlighting, with
some photographs of similar installations. It is necessary to obtain full
planning permission under the Town and County Planning Act 1971
to erect towers, columns or masts for floodlighting in any area.
Application for outline and final planning permission must be made
through local council offices and will require quite detailed
information. Generally, the more comprehensive the information the
less likelihood there will he of delays in receiving approval. An
application may take up to two months and it is wise to consider this
matter before placing any orders.
Fig 89 Seek planning permission
at an early stage of design
It is usually wise to include an illuminance survey indicating the lighting level over the active area with the
'cut-off' beyond this area. This can be shown using a computer luxplot extending beyond say the pitch or
sports area. This printout should where applicable extend to include all affected residential properties, and
demonstrate how the illumination level is reduced to an acceptable level.
Spill light falling onto residential properties should be discussed with the planning officer. Many
residential street lighting schemes produce a lighting level of 5-10 lux measured on the house frontage
adjacent to the light source. In many instances this may be an acceptable limit for the proposed
floodlighting system and may persuade the planning officer to accept the scheme.
Once the necessary planning permission consent has been obtained, a time limit is usually placed on the
consent. Should planning permission be refused, it is sometimes possible to submit a new application
amending the presentation to take account of the reasons for refusal. Finally, if repeated refusal is
encountered and you believe your case to be correct it is possible to appeal to the Secretary of State for the
Environment. Should you decide on such a course of action it is essential to retain a professional
consultant to act for you.
Negotiations with supply authority
Preliminary discussions should be held at an early stage with the local electricity company for large
installations. This is to ensure that it will be able to provide a suitable supply, if it requires a contribution
to the cost of any new capital works to provide the supply, to determine the tariff and to discuss the point
of supply. If the scheme is a major one, the electricity company may hesitate to accept a large load which
will he used only for short periods. However, if the load is required only during off-peak periods when the
industrial load is reduced there should be no difficulty.
Following the completion of the floodlighting installation the electrical contractor should provide the
client with two certificates, both issued by the National Inspection Council for Electrical Installation
Contracts and also available from the Electrical Contractors Association (ECA). The first form is an
inspection and testing certificate on which all relevant tests are
recorded to ensure that the installation complies with the latest IEE
(Institution of Electrical Engineers) regulations. The second form is a
completion certificate certifying the name of the installation
contractor, the scope of work carried out, and confirming that tests
have been completed in a satisfactory manner in accordance with IEE
regulations.
The forms should be forwarded to the local electricity company with
copies to the client. It is recommended that this is included as a
condition of the contract with the installer. If the installation has not
43
Fig 90 Early discussions with the
local electricity company
Floodlighting
been carried out by a member of the National Inspection Council for Electrical Installation Contracts
(NICEIC) the local electricity company should be asked to carry out the necessary tests and complete the
testing completion certificates.
5
Floodlighting System Commissioning
A vital part for any floodlighting installation is the commissioning procedure, which involves aiming,
illuminance and other checks if appropriate. All floodlighting projects require some form of aiming
procedure, for building floodlighting this may simply be a visual check to ensure there is good modelling
or accent of the building. However, for a major or minor sports area the aiming procedure is usually
followed by illuminance measurements.
Aiming floodlights
Clearly there is little point in carrying out involved calculations, possibly on a computer to optimise a
scheme if care and attention is not made to the accurate aiming of the floodlights. Aiming with a precision
floodlight with a beam of maybe 2 or 3° is likely to be more important than that for a general floodlight
with a considerably wider beam. Although to ensure the best performance and reduce spill or obtrusive
light the aiming process should be carried out with care for all types of floodlight. As part of the design
process, and at an early stage of installation, the position and type of each floodlight within structures,
such as gantries or columns, must be clearly conveyed to the installer.
Various techniques and methods have evolved over the years to produce the best method for floodlight
aiming. This has now evolved into two clear-cut methods, dictated by the type of structure employed - it is
not now necessary to carry out aiming by night.
Fixed position mast and gantries
Having produced a detailed aiming pattern over the space to be lit,
the area has markers accurately positioned for each floodlight aiming
point. The best markers are small aluminium tiles 150mm × 150mm
which are both heavy enough to not be blown by the wind and large
enough to be visible from the largest structures. Stakes or pegs are less
suitable as these are not so visible, may damage the surface (such as
Astroturf) and present a hazard if not collected on completion. The
position of the markers is best determined by a measuring wheel
starting from the natural boundaries of the area, for example, the
touchlines and goal lines, as X-Y axes. The peak intensity from the
floodlight is normally used to align with the marker.
Fig 91 Floodlights should be
locked in the right position
An aiming sight is fitted to the floodlight front glass/frame, the floodlight is then adjusted in elevation and
azimuth so that the view through the aiming sight aligns with the marker. Aiming sights are available
throughout the Thorn Group. Allowance should be made if the peak intensity does not occur at 90° to the
front glass, this can be checked by referring to the photometric data. Some floodlights have a built in sight,
rather like that on a rifle, which can be used instead, as with the PRT2000. The ball-bearing and large
graduations on some floodlights will only give approximate aiming and are not suitable for “precision
aiming“.
It is of paramount importance that the floodlight is locked in the right position with both azimuth and
elevation nuts tightened to the correct torque setting. Generally the large hole (about 22mm diameter) in
the stirrup is used - it is important that a large stainless or plated nut and bolt together with washers and
shake-proof washers are used. The size of the bolt should be almost the same diameter to that of the hole
to maximise rigidity, (see installation sheets). It is a good idea to mark with paint a small stripe on the
mounting gantry and floodlight to ensure that the correct aiming may be secure if the floodlight has to be
disturbed.
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Floodlighting
Raising & lowering masts
This is a more complex operation and requires a large protractor, spirit level and variable protractor with
bubble gauge (PBG) or clinometer (army mortar sight). The mast should be lowered until the mast is
level, the floodlight should then be set as though it was to be aimed straight across the area to be lit. The
PBG or clinometer are set to the required elevation aiming angle - making allowance for the position of
the peak intensity relative to the front glass. The floodlight can then be adjusted in azimuth using the large
protractor with the stirrup of the floodlight as reference relative to the supporting bracket/cross arm. The
angle required may be left or right from the straight across position. As raising and lowering these
structures is very time consuming it pays to obtain the correct aiming first time!
A visual check (usually at night or dusk) can be carried out by the observer using dark glasses and standing
slightly forward of the aiming position looking both towards the floodlight and to his shadow behind,
relative to the marker for his exact position. The floodlight is aimed in the correct angles if the reflector
appears “fully flashed”. This procedure needs some practice to be successful.
For building or architectural lighting the visual effect is the requirement that is best checked by trials
following a specific plan for the lighting. The position of the floodlight and aiming should be carefully
noted. On completion of the installation “tweaking” will almost surely be needed to obtain the desired
effect. In particular, care must be exercised in predicting the aiming pattern for recessed floodlights, such
as Mica, where clearly moving the floodlights, post installation, is not a practical method.
Illuminance measurements
These measurements are of course of high importance and may have contractual implications for the
scheme. A high quality light meter should always be used. This should be colour corrected for the
prescribed response for the human eye and also be cosine corrected to make allowance for any light
appearing at a glancing angle to the photocell. Each Thorn region has access to a high quality Hagner
meter, which has the necessary quality criteria, however, the meter requires annual checks against an
intensity standard. The meter should only be used if within the calibration period.
A number of illuminance readings should be made evenly spaced across the area in question. The
measurement points (and number) should have been agreed with the customer during the design phase.
For example a typical grid for soccer would be 8 points across by 11 over the length - these now often
encompass the touchlines. The points can be determined accurately using a surveying circular
measurement wheel or large tape measure - markers can again be used at each measurement position.
For recreational sports, general area lighting or training areas horizontal illuminance is usually used and
the photocell is carefully placed onto the area - care should be exercised to avoid shadows from the persons
carrying out the measurements. For higher level sports lighting, and particularly if TV is to be used,
vertical illuminances at each point will be required. Vertical illuminances are usually determined at about
1.2m above the playing surface and in 4 planes parallel to the boundaries of the area, or if known, normal
to the TV cameras.
This is best carried out using a special tripod with gimbals obtained
from the Thorn Lighting Technology Centre at Spennymoor.
The average illuminance, uniformity and diversity can be determined
from all the measurements, uniformity is usually described as:
Minimum Illuminance
Average Illuminance
Diversity as:
Minimum Illuminance
Maximum Illuminance
Fig 92 Vertical illuminance
measured for televised sports
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Floodlighting
The voltage at each luminaire location should also be recorded, particularly important if illuminance
results are below expectation. A 1% drop in voltage can produce a 3% reduction in light output. A much
higher voltage (+10%) could result in damage to the floodlights and the lamp will have a much shorter life.
If a 3-phase electrical supply is utilised each phase should be measured at each location.
Questions 3
1.
What are two lighting problems that are frequently associated with industrial sites?
2.
What type of lighting is usually used on building site and what is special about it?
3.
Who can provide expert advice on the classification of hazardous areas?
4.
What are the two main functions of sales areas lighting?
5.
Where are the current recommendations for the illuminance of car parks to be found?
6.
What are the six sports categories of play that the CIBSE Lighting Guide No. 4 (1999) recognizes?
7.
After installation of a floodlighting project what certificates should the Electrical Contractor issue?
8.
After aiming and fixing floodlights in the right position how can it be made easy to restore that
position should the floodlight be disturbed?
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Floodlighting
6
Answers to Questions
Questions 1
1. Between 83 and 95 grid points.
2. Primary floodlighting from one side to cast shadows from the vertical features and secondary
floodlighting of about 1/10 intensity from the other side to soften the shadows. This will give form to
the facade so it will not appear flat.
3. The CIE recommends a glare rating of 50 for televised sports events.
4. Louvres, hoods and spill rings can be added to floodlights to give additional light control.
5. Maximum cable length, 17.4m for 2.5mm2 twin and earth flat section cable between a G53282/B
ignitor and a 400W HPS lamp.
6. Type 3 MCB, 25A rating.
7. The light output of lamps may be significantly reduced by small reductions of voltage. A remedy at the
design stage is to specify suitable voltage tapped ballasts.
8. 2-hour and 4-hour average life and lumen maintenance lamp characteristics.
Questions 2
1. Beam data, Intensity curve, isolux diagram, isocandela and zonal flux diagram.
2. Double asymmetrical.
3. 24 lux.
4. SHR = 4 opposite, SHR = 1.5 subject to site conditions.
5.
6.
7.
8.
2 × 339
( 1000 - 0.65) × 17500 = 490 lm
8
10
10
OP =
,
= tan (POG), POG = tan -1 ( 8 . cos 60°) = 32°
cos 60° OP
17.5 × 60 × cos351 ×0.8
E=
= 3 lux
82
20 lux
Questions 3
1. The multiplicity of shadows caused by the nature of the site, and the fact that the visual tasks occur on
planes other than the horizontal.
2. Special linear fluorescent or tungsten halogen luminaires are usually used operated at 110V.
3. The Authority Licensing Board, Factory Inspectorate and the local Fire Officer.
4. To advertise the presence of the place and to enable customers to examine and purchase the goods.
5. BS5489: Part 9: 1996
6. Recreational, supervised training and practice, club, county, national and international.
7. An inspection and test certificate and a completion certificate.
8. By painting a small stripe on the mounting gantry and the floodlight after fixing in the right position.
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Floodlighting
7
Summary
Lighting Objectives and Criteria
Objectives
Lighting objectives can include needs such as to:
• allow safe movement of pedestrians, bikes, cars, and trucks on sites
• attract tourists
• allow the extended use of sports facilities
• deter thieves or vandals.
Associated with these and other objectives are different lighting design criteria, and also different lighting
techniques to satisfy them.
The three broad lighting design objectives of safety, performance, and appearance apply to
floodlighting.
Criteria
• Illuminance and uniformity
• Direction of lighting & modelling
• Maintenance
• Maintained Illuminance
• Atmospheric losses
• Disability and discomfort glare
• Light source colour
• Stroboscopic effects
Floodlighting Equipment
Optical characteristics
The light distribution from floodlights is classified into three groups:
• symmetrical,
• asymmetrical, and
• double asymmetrical.
There are further elements of light control feature in some floodlights.
• Auxiliary reflectors
• External elements, such as louvres, hoods, and spill rings.
• Front moulded glass lenses or stippled diffusers to enable a variety of light distributions.
A distinction is often made between area and precision floodlights.
Columns, masts and towers
Columns or masts are typically 4-30m for mounting luminaires outdoors:
• Up to 12m there is a strong case for the use of columns,
• Between 12 m and 30m the choice depends on the quantity of equipment to be supported
• Above 30m towers or heavy duty masts are used.
Some of the types of metal column available are:
• Flange plate mounted
• Root mounted
• Raising and lowering type
• Hinge type
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Floodlighting
Masts up to 30m are used extensively in large areas, such as docks and lorry parks.
Masts above 50m are normally have an internal ladder with the luminaires mounted on a headframe.
A lattice tower may be an economic alternative to a single mast.
Adequate foundations are necessary, and all structures must be able to withstand the wind forces likely to
be experienced. The specification of foundations is the domain of structural engineers. Lighting
manufacturers can provide data on the weight and windage of luminaires.
Lamps
The 2-hour switching cycle may age lamps three times faster than the 10-hour cycle.
It is useful to know the 2-hour, 4-hour and 10-hour switching cycle average life and lumen maintenance.
Discharge lamps
Metal halide (elliptical and tubular)
Metal halide (linear double ended)
Metal halide compact
Compact source iodide (CSI)
High pressure sodium (elliptical and tubular
High Pressure Mercury
Low Pressure Sodium
Tubular and Compact Fluorescent
Filament Lamps
Linear tungsten halogen
Compact tungsten halogen
Ignitors and transformers
Discharge lamps that require a higher voltage than that of the mains supply may be started by electronic
ignitors or step-up transformers. Ignitors generate a series of high-voltage pulses that cease when the lamp
starts.
Fuse ratings
The correct fuse for a high pressure discharge lamp, is determined by the starting condition, when higher
than normal supply currents will flow. Three current conditions must be allowed for:
• Capacitor inrush current
• Current due to rectification
• Run-up current
Capacitor inrush current
The transient inrush current can be up to 25 times the normal capacitor current but only lasts for about a
millisecond. To allow for this it is recommended that fuses supplying circuits containing capacitors should
be rated at 1.5 times the normal capacitor current. (The normal capacitor current at 230/240V 50Hz is the
capacitor value in µF multiplied by 0.076A).
Current due to rectification
For a short period after starting a discharge lamp may act as a partial rectifier, allowing DC current to
flow. The effect of this DC is to saturate the iron core of the ballast and reduce the impedance allowing a
current of several times the normal value to flow. This transient condition does not always happen and
that the degree of partial rectification will vary from lamp to lamp and from time to time.
Starting current
After the initial starting period there is a run-up time of several minutes, the maximum value of the supply
current that flows during the first minutes is referred to as the supply starting current and is given in
Table 1 (page 14 and on).
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Floodlighting
Fuse ratings for single lamp circuits
Table 2 with each lamp type (page 14 on), gives the recommended fuse ratings for a single lamp circuit.
These values are based on possible rectification currents that need to be allowed for.
Fuse ratings for installation of more than one lamp
Starting current and capacitor inrush current predominate and are used to calculate these fuse
rating. (Table 2)
Voltage Variation
Lower voltages affect a floodlighting system. The further away floodlights are from the switchroom the
greater the voltage-drop. The light output from some discharge lamps may vary at a rate four times
greater than the applied voltage. 1% voltage reduction can produce a 4% reduction in light output.
Control gear housings
Banks of gear mounted remotely in one enclosure should have ballasts spaced well apart in all directions
and be adequately ventilated. Control gear should preferably be mounted close to the lamp or lamps, in
the luminaire itself, in the base compartment of the column or in a rainproof control box.
Floodlighting data and calculations
Beam data shows:
• Peak intensity
• Beam factor to 10%, horizontal and vertical angles
• Beam factor to 50%, horizontal and vertical angles
• Beam factor to 1%, horizontal and vertical angles
Intensity curve
Used to see intensity characteristics and finding intensity at various angle in cd/1000lm.
Isolux diagram - For a specified mounting height, on a grid in metres contours of constant illuminance
are shown in units of lux/1000 lm.
Utilisation Factor - UF = Waste Light Factor × Beam Factor = WLF × BF
Thorn Floodlighting Calculator is a better choice for preliminary designs than using a UF of 0.3 if a
rectangular area is to be lit.
Layout and mounting height
Single side floodlighting typical area lit 3 × mounting height without large obstructions.
Single side floodlighting area lit 5 × mounting height with no obstructions.
Single side floodlighting area lit 2 × mounting height with obstructions.
Double side floodlighting typical area lit 6 × mounting height without large obstructions.
Transverse spacing typically 2 × mounting height.
Zonal flux diagram
It provides a more accurate way of determining utilsation factors for floodlighting schemes. The number
in a particular grid square is the flux emitted per thousand lamp lumens in the zone defined by the two
pairs of vertical and horizontal angles forming the grid square. It can be used to find average illuminance
over a lit area.
Isocandela diagram
Used for illuminance at a point. A value of intensity in cd/1000lm read from the diagram can be inserted
into an inverse square law formula.
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Floodlighting
Lighting design software
Lighting design software can be useful for complex projects where many repetitive calculations must be
carried out to find the uniformity of illuminance on the horizontal, vertical, or inclined planes, using such
programs as:
Thorn Lighting TL Vision
Thorn Lighting Optilume Flood
Floodlighting Applications
Industrial
Outdoor industrial sites often have two lighting problems, the multiplicity of shadows caused by the nature
of the site, and the fact that the visual tasks occur on planes other than the horizontal. Information of the
likely or actual obstructions is needed to select the mounting height and location of floodlighting positions
to minimize shadows.
Building sites
Low voltage supplies of 110 V or below are usually mandatory at building sites for all equipment that is
accessible to site workers. Only special linear fluorescent or tungsten halogen luminaires can be used for
temporary site lighting.
Cargo handling, stock yards and docks
Light obstruction can be a major design problem. Floodlights mounted on high masts or towers, or on site
buildings, can provide the general lighting for safe movement with local task lighting for the handling of
goods being achieved by projectors mounted on the crane structures.
Hazardous areas
Expert advice on the classification of areas is available from the Authority Licensing Board, Factory
Inspectorate and the local Fire Officer.
Select products by:
• Zone
• Gas Group
• T Rating
• IP Rating
Quarries
The dimensions of quarries change. As the floodlighting installation will probably be permanent, the
design should be based on the ultimate size of the excavations. Additional floodlights can be installed as
excavation increases.
Security lighting
The prime objectives of security lighting are to deter criminal activity or, if that fails, to detect and prevent
it. For public areas, the lighting provides general amenity to give a feeling of safety and well being while
enabling security staff to monitor potential or actual criminal activity.
There are five basic lighting techniques, which can be adapted to suit almost any situation:
• Perimeter lighting
• Checkpoint lighting
• Area lighting
• Floodlighting
• Topping up
Commercial
The aim of commercial floodlighting is to provide amenity in public areas and create an attractive
night-time visual environment rather than providing for exacting visual tasks to be performed: lighting
aimed at promoting sales, leisure or tourist activities or at expressing civic pride or corporate status.
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Floodlighting
Sales areas
The floodlighting of exterior sales areas serves two main functions:
• to advertise their presence, and
• to enable customers to examine and purchase the goods.
Consider district brightness, vertical illuminance, directional and colour qualities of lighting.
Car parks
Use BS5489: Part 9 1996 Recommendations for illuminance. Preliminary layout lighting a depth 3 ×
mounting height and lateral spacing 3 × mounting height. Column heights may vary between 3m and
12m. Height should be kept in scale with surroundings.
Lorry parks
Lorry parks are most satisfactorily lit from the perimeter of the area to reduce the risk of damage to poles
and floodlights caused by vehicles. Perimeter floodlights should be mounted at least 12m from the ground
to reduce shadows.
Sign lighting
The quantity of light required from floodlights to illuminate signs will depend on the:
• size of the sign,
• distance from which it is viewed,
• contrasts of various parts of the sign with each other,
• and the ambient lighting conditions.
To obtain a reasonable uniformity of illuminance along the length of a sign, luminaires bracketed from
above should be spaced laterally at between 2.5 and 3 times the bracket length, provided that asymmetric
wide angle floodlights are used.
Buildings
Complete facade should be illuminated to some extent in order to show the entire building outline to the
viewer. Its solidity can be emphasised by adding light at a lower illuminance to the side.
There are broadly four architectural styles for building facades requiring different lighting treatments:
• Facades that are basically flat
• Facades with predominantly vertical characteristics
• Facades with predominantly horizontal characteristics
• Facades with external recesses
These average luminance can be considered:
• rural sites with little or no road lighting and competition from other illuminated buildings and signs up to 5 cd/m2,
• towns and suburban areas with medium district brightness - 5 to 10 cd/m2,
• city centres and other brightly lit areas - 10 to 15 cd/m2.
Sports
CIBSE Lighting Guide No. 4 (1999) recognizes up to six categories of play:
• recreational
• supervised training and practice
• club
• county
• national
• international
Some sports, e.g. tennis, soccer, rugby and baseball that are played on areas for which the dimensions are
closely specified so lighting with standard floodlight layouts can to be recommended.
For sports in large stadia where TV coverage is required, illuminance related to the camera takes priority.
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Floodlighting
Lighting near airports
Part 8 of BS5489 Road Lighting gives recommendations for lighting within defined areas around
aerodromes, railways, harbours and navigable waterways, additional to the general recommendations of
other parts of BS5489.
Solar simulator
Floodlights can be used to create an 'artificial sun', to mimic the luminous intensity and power of the sun
over a small area. Typical applications have been the testing of solar panels and various materials used in
the aircraft industry, for example the nose cones of new jet fighters.
Planning permission
It may be required for all exterior floodlighting schemes. At the initial stages of floodlighting determine
‘in principle’ if planning consent will be granted for the proposed floodlighting. It is necessary to obtain
full planning permission under the Town and County Planning Act 1971 to erect towers, columns or
masts for floodlighting in any area. A time limit is usually placed on planning consent.
Negotiations with supply authority
At an early stage of large installations discussions should be held with the local electricity company.
After completion of the installation the electrical contractor should provide the client with two certificates,
both issued by the National Inspection Council for Electrical Installation Contracts (NICEIC) and also
available from the Electrical Contractors Association (ECA):
• inspection and testing certificate
• completion certificate
Floodlighting System Commissioning
Commissioning procedure of a floodlighting installation involves aiming, illuminance and other checks.
Fixed position mast and gantries
• Markers are accurately positioned for each floodlight aiming point
• An aiming sight is fitted to the floodlight front glass/frame
• The floodlight is adjusted in elevation and azimuth so that the view through the aiming sight aligns
with the marker.
• The floodlight is locked in the right position with both azimuth and elevation nuts tightened to the
correct torque setting.
• Paint a small stripe on the mounting gantry and floodlight for correct aiming if the floodlight is
disturbed.
Raising & lowering masts
This requires a large protractor, spirit level and variable protractor with bubble gauge (PBG) or
clinometer (army mortar sight).
•
•
•
•
•
Lower the mast until level
Set the floodlight as though aimed across the area to be lit
The PBG or clinometer are set to the required elevation aiming angle
The floodlight can then be adjusted in azimuth using the large protractor
It is best to obtain the correct aiming angles first time
A visual check at night or dusk can be done by the observer using dark glasses and standing slightly
forward of the aiming position looking both towards the floodlight and to his shadow behind, relative to
the marker for his exact position. The floodlight is aimed in the correct angles if the reflector appears
“fully flashed”.
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Floodlighting
Illuminance measurements
A high quality light meter should always be used. This should be colour corrected for the prescribed
response for the human eye and also be cosine corrected to make allowance for any light appearing at a
glancing angle to the photocell. The meter should only be used if within the calibration period.
The measurement points (and number) should have been agreed with the customer during the design
phase. The points can be determined accurately using a surveying circular measurement wheel or large
tape measure - markers can again be used at each measurement position.
The voltage at each luminaire location should also be recorded, particularly important if illuminance
results are below expectation.
54