MECH3005 – Building
g Services
http://www.hku.hk/bse/mech3005/
Lighting System Design –
Design Methods
Dr. Sam C M Hui
Department of Mechanical Engineering
The University of Hong Kong
E-mail:
E
mail: cmhui@hku.hk
cmhui@hku hk
Sep 2010
Content
• Basic Principles
• Design Process
• Design Factors & Issues
• Lighting Calculations
Basic Principles
• Three main functions of lighting:
• Ensure the safety of people
• Facilitate the performance of visual tasks
• Aid the creation of an appropriate visual
environment (appearance & character)
Basic Principles
• Two sources of light:
• Natural sources of light (daylight)
• People prefer daylight to “windowless” rooms
• Windows provide a view & connection to outdoor
• Artificial or man-made (electric light)
• El
Electric
i lighting
li h i andd the
h daylighting
d li h i should
h ld be
b
p
y to ensure
complementary
• Efficient use of energy
• High
i h quality
li lighting
li h i
General lighting
[Source: CIBSE Lighting Code]
Localised lighting
[Source: CIBSE Lighting Code]
Local (task) lighting
[Source: CIBSE Lighting Code]
Set the goals
Specify criteria
S t type
System
t
Calculations/
detailss
deta
V ifi i
Verification
Lighting design and planning
[Source: CIBSE Lighting Code]
Design Process
• Basic approach to lighting design
• Determine lighting design criteria
• Quantity of illumination (lighting level, lux)
• Quality of illumination (e.g. overall appearance, colour)
• Codes and regulations (e.g. building, electrical, energy)
• Record architectural conditions & constraints,
constraints e.g.
eg
• Window location & size, ceiling height, finish materials
• Determine visual functions & tasks to be served
• Select lighting system to be used
Design Process
• Basic approach to lighting design (cont
(cont’d)
d)
• Select luminaire and lamp types
• To produce the desired light & fit the client’s needs
• Determine number & location of luminaires
• Through calculations & assessment
• Place
Pl
switching
it hi & other
th control
t l devices
d i
• User convenience & energy management
• Aesthetic & other intangibles
• Aesthetic & psychological factors
Design Process
• Typical lighting controls
•
•
•
•
•
•
•
Switches
Occupancy sensing
Scheduling (timeclocks)
Daylight dimming
Tuning
Preset dimming
Building management
Design Factors & Issues
• Important
p
to consider:
• Situation – is it a working, viewing, circulation or
a living space?
• Function – what will people do in the space?
• Quantity and Quality of Light – what's needed to
perform the tasks?
• Architecture and Décor – consider the aesthetic of
p
the space
• “Atmosphere” – what is the mood or ambience of
the space?
Design Factors & Issues
• Lighting
g
g qquality
y and criteria
• Lighting level (lux or luminance e.g. road lighting)
• Luminance
L i
distribution
di t ib ti
• Better distribution of brightness within the field of view
• Freedom from disturbing glare
Spatial
a ddistribution
st but o oof light
g t
• Spat
• General lighting, directional lighting, backlighting and
p g
g, diffuse lighting
g
g
uplighting,
• Light colour and colour rendering
• Colour temperature and colour rendering index
Design Factors & Issues
• Directional effects (form,
(form dimension & texture)
• Direction and distribution of light within a space
• Influence perception of the space
• Relates partly to desirable illumination levels and partly
to architectural style and visual emphasis
• Good light
g design
g - an appreciation
pp
of the nature and
qualities of the surfaces
• Modelling – ability of light to reveal solid form
• Fail to do that will result as bland and monotonous
• Emphasis – e.g. surface texture & characteristics
Examples of directional effects in lighting design
Design Factors & Issues
• Glare 眩目光
• Occurs when objects, seen directly or by reflection,
are too bright c.f.
c f the general background
• Disability glare - impairs ability to see detail w/o
necessarily
il causing
i visual
i l discomfort
di
f t
• Shift in adaptation level
• Discomfort glare - causes visual discomfort w/o
necessarily impairing vision
• Depends on occupant’s activity, angle of view, size and
brightness of source, average luminance of background
Bright light entering
from a window
Veiling reflection from
overhead light source
Examples of glare and veiling reflection
Design Factors & Issues
• Reduce glare from artificial light sources
• Limit the luminance of sources in eye’s direction
• Replace a bright source with few weak sources
• Restrict light distribution to  sideways light to the eye
• Screen the sources from view
•
•
•
•
Introduce downstand screens
Use screening within the fitting (e.g. louvres)
Enclose source in light diffusing panel/fitting
Conceal fittings from view (e.g. by beams)
Design Factors & Issues
• Reduce glare from artificial light sources
(Cont’d)
• Re-position the work station to avoid glare
• Raise background luminance
• Use fittings with more upward flux (brighten ceiling)
• Specify
S if higher
hi h reflectance
fl t
floor
fl
• Use light-coloured finishes
Design Factors & Issues
• Reflected glare & veiling reflection
• Bright patches on glossy surfaces from reflection
• Reflected glare - produce visual discomfort
• Veiling reflection - reduce contrast and visibility
• May be minimised by:
• Ensure no part of the task is at or near the mirror angle
with respect to the eye & bright source
• Increase
I
light
li ht falling
f lli sideways
id
onto
t the
th visual
i l task
t k
• Use luminaires w/ large surface area & low luminance
• Use paper, machines, materials etc. with matt surfaces
Glare control for video display unit (VDU)
[Source: CIBSE Lighting Code]
Lighting Calculations
• To calculate the amount of light that will
result from a design
• Critical for commercial & institutional buildings
• Seldom required for residential design
• Basic considerations
• Light sources (lamp lumens)
• Luminaires & light distribution
• Initial vs. maintained light levels (as lamps age
and luminaires get dirty, light level drops)
Lighting Calculations
• Predict general & ambient light levels
• Rough estimation based on a Watts/sq.m method
• Not very accurate, but good for prelim. planning
• Lumen method calculations
• Average illuminance
• Good for general lighting
• Point-by-point computer calculations
• Most complicated, start from fundamental laws
• Can be used for outdoor lighting
g
g
Rough estimation based on a Watts/sq.m method
Average light level desired &
typical application
Watts/sq.m
Watts/sq
m of
fluorescent, CFL or
HID lights
Watts/sq.m
Watts/sq
m of
incandescent or
halogen lamps
25-50 lux
Hotel corridors, stair towers
1-2
3-7
50-100 lux
Office corridors, parking garages,
theatres (house lights)
2-4
7-10
100-200 lux
g lobbies,, waiting
g areas,,
Building
malls, hotel function spaces
4-8
10-20
200-500 lux
Office areas, classrooms, lecture
halls, conference rooms, ambient
g
g, workshops
p
retail lighting,
15-25
Not recommended
500-1000 lux
Grocery stores, laboratories, work
areas, big box retail stores
12-20
Not recommended
[Source: Adapted from Karlen and Benya, 2004. Lighting Design Basics]
Lighting Calculations
• Lumen Method: average
g illuminance ((E)) is
F  n  N  UF  MF
E
A
•
•
•
•
•
•
F = initial bare lamp luminous flux (lumens)
n = number of lamps per luminaire
N = number of luminaires
UF = utilisation factor
MF = maintenance factor
A = area off the
th surface
f
(m
( 2)
Lighting Calculations
• Utilisation factor (UF)
( )
• Ratio of total flux received by the surface to the
total lamp flux of the installation
• UF tables are prepared for general lighting with
regular
l arrays off luminaires,
l i i
for
f 3 main
i room
surfaces: ceiling cavity, walls, and floor cavity or
h i t l reference
horizontal
f
plane
l
• Maximum spacing
p
g to height
g ratio ((SHRmax)
• Luminaire spacing shall not exceed the max. to
ensure uniformity
Lighting Calculations
• Room index ((K):
) a measure of the proportions
p p
of the
room, for rectangular room
• K = (L x W)/(L + W) hm
• L = length of the room
• W = width of the room
• hm = height of luminaire above horiz. reference plane
• Effective
Eff ti reflectances
fl t
off ceiling,
ili walls
ll & floor
fl
• Cavity index (CI) = (L x W)/(L + W) h = K x hm/h
• h = depth of the cavity (ceiling or floor)
• Determine effective reflectance from tables or formulae
(see examples in CIBSE Lighting Code)
R
Recommended
d d room reflectances
fl
& illuminance
ill i
ratios
i
[Source: CIBSE Lighting Code]
Lighting Calculations
• Maintenance factor (MF)
• Ratio of maintained illuminance to initial
ill i
illuminance
(losses
(l
for
f lamp
l
lumen
l
maintenance)
i
)
• MF = LLMF x LSF x LMF x RSMF
•
•
•
•
Lamp lumen maintenance factor (LLMF)
Lamp survival factor (LSF)
Luminaire maintenance factor (LMF)
Room surface maintenance factor (RSMF)
• See CIBSE Code off Lighting
g
g for description
p
Lighting Calculations
• Lumen method: calculation procedure
• Calculate room index K, floor/ceiling cavity index
• Calculate effective reflectances of ceiling cavity, walls &
fl
floor
cavity
it
• Determine utilisation factor (UF) from manufacturer's data,
using the room index and effective reflectances
• Determine maintenance factor (MF)
nos. of luminaires required (using lumen method)
• Obtain nos
• Determine a suitable layout
• Check that the geometric mean spacing
spacing-to-height
to height ratio
• Check the layout does not exceed SHRmax
• Calculate illuminance achieved by
y the final layout
y