Basics of Light and Lighting
Basics of Light and Lighting
Lighting concepts
Basics of Light and Lighting
What is light?
Light and radiation
Light is a form of energy manifesting itself as
electromagnetic radiation and is closely related to other
forms of electromagnetic radiation such as radio
waves, radar, microwaves, infrared and ultraviolet radiation
and X-rays.
Light is the electromagnetic radiation that the human eye
perceives as brightness, in other words the part of the
spectrum that can be seen. This is the radiation between
380 and 780 nanometres (nm), a tiny fraction of the known
spectrum of electromagnetic radiation.
Lighting concepts
Basics of Light and Lighting
Basic parameters used in lighting
Luminous flux (F)
Unit of measurement: lumen (lm)
All the radiated power emitted by a light source
and perceived by the eye is called luminous flux
(F).
• 75W incandescent lamp: 900 lm
• 39W fluorescent lamp: 3.500 lm
• 250W high pressure sodium lamp: 30.000 lm
• 2000W metal halide lamp: 200.000 lm
Luminous intensity (I)
Unit of measurement: candela (cd)
Generally speaking, a light source emits its luminous flux (F) in different
directions and at different intensities. The visible radiant intensity in a
particular direction is called luminous intensity (I).
Examples (centre of beam):
• 5W bicycle lamp without reflector: 2,5 cd
• 5W bicycle lamp with reflector: 250 cd
• 120W incandescent reflector lamp: 10.000 cd
• Lighthouse: 2.000.000 cd
Lighting concepts
Basics of Light and Lighting
Basic parameters used in lighting
Luminance(L)
Unit of measurement: cd / sqm
Luminance is the only basic lighting parameter that is perceived by the eye.
It specifies the brightness of a surface and is essentially dependent on its
reflectance (finish and colour).
Examples:
• Surface of the sun: 1.650.000.000 cd/m2
• Filament of a clear incandescent lamp: 7.000.000 cd/m2
• Fluorescent lamp: 5000-15.000 cd/m2
• Road surface under artificial lighting: 0,5-2 cd/m2
Illuminance (E)
Unit of measurement: lux (lx)
Illuminance (E) is a measure of the amount of light falling on a surface. It
is influenced by the distance the light source is away from the area being
illuminated. An illuminance of 1 lux occurs when a luminous flux of 1
lumen is evenly distributed over an area of 1 square metre.
Examples:
• Summer, at noon, under a clear sky (equator): 100.000 lux
• In the open under a heavily-overcast sky: 5.000 lux
• Artificial light, in a well-lit office: 800 lux
• Full moon, on a clear night: 0,25 lux
Lighting concepts
Basics of Light and Lighting
Basic parameters used in lighting
Luminous efficacy
Unit of measurement: lumens per watt (lm/W)
Luminous efficacy indicates the efficiency with
which the electrical power consumed is
converted into light.
Luminaire efficiency
Luminaire efficiency (also known as the light output
ratio) is an important criterion in gauging the energy
efficiency of a luminaire. This is the ratio between the
luminous flux emitted by the luminaire and the
luminous flux of the lamp (or lamps) installed in the
luminaire.
Lighting concepts
Basics of Light and Lighting
Basic parameters used in lighting
Lamp Life
Because of slight variations in lamp materials and manufacturing operations, lifetimes of
individual lamps differ. The term ‘lamp life’ usually refers to the ‘average rated life’ of a
lamp. This is the time after which, on statistical average, half (50%) of a ‘not too small’
number of lamps fail in a controlled operating environment. Each of the lamps in the test
group should be of the same wattage, voltage and construction.
Lighting concepts
Basics of Light and Lighting
Basic parameters used in lighting
Colour Appearance & Colour Rendering
Light sources have two different colour properties related to the spectral composition of
their emission. One is the apparent colour of the light that the source emits and the other
is the effect that the light has on the colours of surfaces. The latter is called colour
rendering.
When a light source is being chosen, both the colour appearance and the colourrendering properties of the source should be considered in addition to its efficacy and life.
Lighting concepts
Basics of Light and Lighting
Basic parameters used in lighting
Colour Appearance
The colour appearance of near white light sources is normally
defined in terms of their correlated colour temperature (CCT),
expressed in kelvin (K). The higher the correlated colour
temperature the cooler the appearance of the light source. An
ordinary incandescent lamp, for example, has a colour
temperature of 2800K, whereas a daylight fluorescent lamp
can have a colour temperature of 6000K.
Figure 1: The CIE Chromaticity Diagram
The International Commission on
Illumination (CIE)
has grouped lamps into three classes of
correlated colour temperatures
Colour
Appearance
Group
Colour
Appearance
Correlated
colour
temperature,
K
1
Warm
< 3300
2
Intermediate
3300 < 5300
3
Cold
> 5300
Lighting concepts
Basics of Light and Lighting
Basic parameters used in lighting
Colour rendering
The CIE general colour-rendering index is a measure, on a
scale of up to 100, of the correspondence between the
colour of an object (its “self luminous colour”) and its
appearance under the nearest reference light source.
A light source with an Ra value of 100 displays all 14 test
colours exactly as they appear under the reference light
source. The lower the Ra value, the worse the colours are
rendered.
The CIE general colour-rendering index (CRI) is the most
widely accepted measure of the colour rendering
properties of a light source.
Initial Illuminance
Initial illuminance is defined as the value of average illuminance which is initially provided
by the lighting system, i.e. with new lamps (aged to 100 hours), clean luminaires and
room surfaces.
Lighting concepts
Basics of Light and Lighting
Maintenance factor
Maintenance illuminance is defined as the average illuminance below which it is
necessary to take remedial action in terms of maintaining the lighting system, eg.
by replacing the lamps or by cleaning the luminaires, windows, rooflights and
room surfaces.
The lighting scheme should be designed with an overall maintenance factor (MF)
calculated for the selected lighting equipment, environment and specified
maintenance schedule.
The recommended illuminance
for each task is given as
maintained illuminance. The
maintenance factor depends on the
maintenance characteristics of the
lamp and control gear, the
luminaire, the environment and the
maintenance programme.
Lighting concepts
Basics of Light and Lighting
The illuminance
The illuminance and its distribution on the task area and on the surrounding
area have a great impact on how quickly, safely and comfortably a person
perceives and carries out the visual task.
Scale of illuminance
To give a perceptual difference the recommended steps of illuminance (in lx) are
according to EN 12665:
20 - 30 - 50 - 75 - 100 - 150 - 200 - 300 - 500 - 750 - 1 000 - 1 500 - 2 000 - 3
000 - 5 000
The required maintained illuminance should be increased when:
• visual work is critical;
•errors are costly to rectify;
• accuracy, higher productivity or increased concentration is of great importance;
•task details are of unusually small size or low contrast;
•the task is undertaken for an unusually long time;
Lighting concepts
Basics of Light and Lighting
The illuminance
The required maintained illuminance may be decreased when:
• task details are of an unusually large size or high contrast;
•the task is undertaken for an unusually short time.
Key
1- task area
2 -immediate surrounding (band with a width
of at least 0,5 m around the task area within
the visual field)
3 -background area (at least 3 m wide
adjacent to the immediate surrounding area
within the limits of the space)
Minimum dimensions of immediate
surrounding and background area
in relation to task area
Lighting concepts
Basics of Light and Lighting
The illuminance
Relationship of illuminances on immediate
surrounding to the illuminance on the task area
Measuring level for task area of the workplaces is at 0.75m above floor level !
Lighting concepts
Basics of Light and Lighting
Glare
Glare is the sensation produced by bright areas within the visual field, such
as lit surfaces, parts of the luminaires, windows and/or roof lights.
Glare shall be limited to avoid errors, fatigue and accidents. Glare can
be experienced either as discomfort glare or as disability glare.
Discomfort glare
UGR – stands for Unified Glare Rating
The recommended limiting values of the UGR :
10, 13, 16, 19, 22, 25, 28
Lighting concepts
Basics of Light and Lighting
Electric measuring units
Volt
The Volt (V) is the unit of measurement stabilised by the International System
of Measurement for quantifying differences in electrical potential. It is defined
as the potential difference existing between the extremes of one conductor in
which power of 1 watt is released when current equal to 1 ampere is fluxing
inside.
Watt
The Watt (W) is the unit of measurement of energetic flux and represents the
power emitted, transported or received in the form of radiation.
Ampere
The Ampere(A) is the unit of electric current.
P(power) (Watt) = U(voltage)(volts) x I( current)(amps) x cosØ
Lighting concepts
Basics of Light and Lighting
Terms and definitions
•Activity area - area within which a specific activity is carried out
•Background area - area adjacent to the immediate surrounding area
•Immediate surrounding area - band surrounding the task area within the
visual field
•Roof light - daylight opening in the roof or a horizontal surface of a building
•Shielding angle - angle between the horizontal plane and the first line of sight
at which the luminous parts of the lamps in the
luminaire are directly visible
•Task area - area within which the visual task is carried out
•Visual task - visual elements of the activity undertaken
Work station - combination and spatial arrangement of work equipment,
surrounded by the work environment under the conditions imposed by the work
tasks
Lighting concepts
Basics of Light and Lighting
Luminous environment
Lighting requirements are determined by
the satisfaction of three basic human
needs:
• visual comfort, where the workers
have a feeling of well-being; in an indirect
way this also contributes to a higher
productivity level and a higher quality of
work;
•visual performance, where the workers
are able to perform their visual tasks,
even under difficult circumstances and
during longer periods;
•safety
Lighting concepts
Basics of Light and Lighting
Lighting requirements for interior areas, tasks and activities
Lighting concepts
Basics of Light and Lighting
Lighting requirements for interior areas, tasks and activities
Lighting concepts
Basics of Light and Lighting
Lighting requirements for interior areas, tasks and activities
Lighting concepts
Basics of Light and Lighting
Lighting requirements for interior areas, tasks and activities
Lighting concepts
Basics of Light and Lighting
Lighting requirements for interior areas, tasks and activities
Lighting concepts
Basics of Light and Lighting
Lighting concepts