Lighting

1. 16469
Lighting and Daylighting Design

2. Energy Efficient Lighting
• Lighting accounts for a
significant portion of energy
use in commercial buildings
• We can significantly reduce
this energy use by
- using energy efficient
lighting
- substituting artificial light
with daylight (when
available) [this requires the
use of light sensitive
lighting control]
- minimise the use of lighting
when not required [requires
the use of occupancy
sensing controls]

3. Energy Efficient Lighting

4. Lighting Objectives
• The prime objectives behind the design of a lighting system
are
• the safety and comfort of occupants – the nature of a task
or process performed in a space will dictate the illuminance
level which must be provided by the lighting system (lx or
lm/m2). Tasks involving high degrees of visual acuity will
require higher lighting levels.
• the minimisation of energy consumption –involves the
development of the most energy efficient lighting systems
which is suitable for the task, this can be achieved by
selecting high efficiency equipment and making use of
available daylight.
• colour rendering or the creation of a specific atmosphere
– the colour characteristics of a lighting scheme will affects
tasks performed when the lighting system is on. Tasks which
require the accurate representation of colour require a light
with the spectral characteristics of daylight. Alternatively, to
create a “warm atmosphere” in a restaurant requires the
selection of lights skewed to the red end of the spectrum.

5. Design Stages
A lighting design has several stages. These are as follows:
• Identification of the requirements for the lighting system, illuminance levels,
colour requirements, available space, etc;
• Selection of equipment, lamps, luminaires: lighting systems consist of
numerous components, the two most important of which are: lamps, which
influence the lighting level, colour characteristics and efficiency of the lighting
system; luminaires affect the efficiency with which the light is distributed and so
affect lighting efficiency and uniformity.
• Design of the lighting system: lighting systems are designed to achieve a
reasonably uniform distribution of light on a particular plane (usually horizontal),
avoidance of glare with a minimum expenditure of energy. The most rudimentary
form of lighting design is done using a manual calculation - the lumen method.
However, lighting design is increasingly done using computers.
• System control: once a lighting system has been designed it can be controlled
in such a way as to make maximum use of available daylight, through selection
of appropriate switching mechanisms and daylight responsive controls.

6. Lighting Requirements
Building Area Standard Maintained
Illuminance (lux)
Colour Rendering
Entrance hall 200 -
Corridors 100 -
Kitchens 300 -
General offices 500 -
Drawing Rooms 750 Good colour rendering
may be required
Classrooms 300 -
Lecture Theatres 300 -
Art rooms 500 Excellent colour rendering
required

7. Colour Rendering
Colour
rendering group
CIE colour rendering index
(Ra)
Comments
1A Ra > 90 Used wherever accurate colour
matching is required
1B 80 < Ra < 90 Used when accurate colour
matching is required e.g. clothes
shops
2 60 < Ra < 80 Where moderate colour rendering is
required
3 40 < Ra < 60 Where colour rendering is
unimportant but distortion of colour
is unacceptable
4 60 > Ra Where marked colour distortion is
acceptable e.g. street lighting

8. Selection of Components
• Lamps are selected based on those which are compatible (lamp type, dimensions,
frequency of operation, etc) with the selected luminaire and which have the appropriate
colour-rendering index.
reflector
lamp
casing

9. Selection of Components
• Selection of components follows from the
identification of systems requirements.
• The luminaires are normally chosen first: lighting
catalogues usually describe the uses for particular
types of luminaire, these also come with different
types of reflectors for different applications e.g.
low glare reflectors for computer rooms.
• Reflectors govern the light output characteristic of
a luminaire.

10. Direct Illumination
• Consider a lamp
hanging above a
point A
• The illuminance E
(Lux) is a function
of the intensity of
the lamp I(cd) and
the distance of A
from the source d
• The light from the
source is
perpendicular to A
I
d
A
2
d
I
EA 

11. Direct Illumination
Now consider point B
• The illuminance E
(Lux) is still a function
of the intensity of the
lamp I(cd) and the
distance of B from the
source d’
• However the light
beams no are no
longer perpendicular to
B (they illuminate a
greater area)
I
d
A
2
d
I
EA 
B
θ
d’

12. Direct Illumination
C B
B’
• Considering a small
area around B
• The light from the
source illuminates area
CB
• The component of I
intensity I falling on CB
– I’ is

cos
I
I 

θ
I
Icos

13. Direct Illumination
B
 


2
2
2
2
cos
cos
' d
I
d
I
d
I
EB











• The illuminance on
plane CB’ can be
calculated using
• substituting for I’
 
 
law)
cubed
cosine
(
cos
cos
cos
3
2
2
2



d
I
d
I
EB









14. • The cosine3 law allows us to
calculate direct illuminance from
single of multiple sources
• However in reality illumination is
a combination of direct and
indirect illumination (e.g.
reflections from other surfaces)
• With reflection, accurate
illumination calculations become
exceptionally complex (requires
computer)
• However simplified methods exist
to allow us to calculate the
luminance on a working plane
Direct Illumination

15. Lumen Method
A simple means of calculating illuminance is achieved by means of the lumen
method; this is a simplified design approach to enable the designer to achieve
an even light distribution in spaces of reasonably simple geometry (i.e.
rectangular).
UF
MF
F
n
A
E
N





N - is the number of luminaires
required;
E - is the required illuminance (lux);
A - is the area to be lit;
n - is the number of lamps per luminaire;
F - is the lamp lumen output (lumens);
MF - is known as the maintenance factor,
which is a combination of three factors;
UF - is the utilisation and is a function of
the luminaire properties and room
geometry.

16. Utilisation Factor
• The room geometry is a
crucial factor in determining
the utilisation factor term in
the lumen equation. Several
parameters are important.
– In the lumen method of
design the room
geometry is characterised
by a room index (K)
– The reflectances (ρs) of
surfaces
floor cavity
ceiling cavity
working plane
ceiling plane hm
length L
width W
m
h
W
L
W
L
K
)
( 



17. Manufacturer’s Data
• The utilisation factor can be obtained once the surface reflectances (or effective
reflectances) are known along with the room index (K)
• each luminaire produced by a manufacturer has a lookup table for UF (UF values in
bold):
Reflectances Room Index (K)
Ceiling Wall floor 0.75 1.00 … 5.00
0.7 0.3 0.2 0.45 0.51 … 0.69

18. Maintenance Factors
• The maintenance factor is a value designed to account for the reduction in light output from
a lighting system due to: the ageing of the lamps and the accumulation of dirt and dust on
the light fittings and room surfaces. The MF is therefore time varying and is the product of 4
factors:
• Lamp lumen maintenance factor (LLMF) – a value between 0 and 1 which accounts
for the degradation of lamp output over time
• Lamp survival factor (LSF) – this accounts for the failure of lamps over time, if failed
lamps are replaced immediately this factor can be ignored.
• Luminaire maintenance factor (LMF) – a value between 0 and 1 that accounts for
dirt and dust accumulation on the luminaire. Causes LMF to decrease.
• The room surface maintenance factor (RSMF) - again this is a value between 0 and
1 and accounts for the build up of dirt on room surfaces over time. The build up of dirt
over time causes the RSMF to decrease.
The overall maintenance factor is the product of the four maintenance factors:
MF = LLMF × LLF × LMF × RSMF

19. Lamp Output
Lamp output decreases over time (typically use 2000hr value in design calc)
end of lamp life
lnitial lumen
output
time
lamp output
(lumens)

20. Cleaning
• Cleaning and the cleanliness of the environment also affects lamp
output
end of lamp life
initial lumen
output
time
total output
(lumens)
lamps and
surfaces cleaned
lamps cleaned

21. Grids
• The output from the Lumen Method is a number of lights needed to
achieve the desired illuminance level
• These must be arranged in a grid, the spacing of which is a key parameter
in the design
axial spacing
transverse spacing

22. Spacing to Height
The utilisation factors used in the lumen method are based on a maximum spacing to
height ratio. The spacing to height ratio is as follows:
m
h
spacing
fitting
SHR 
• If the lighting system arrived at has a grid spacing (fitting to fitting spacing)
greater than the maximum (SHR MAX) then the design process must be iterated
as the illuminance (lux) on the working plane will not be acceptable i.e. uneven
“patchy” illumination).

23. Spacing to Height
• Linear luminaires have two spacing to height ratios an axial (SHR AX) and
transverse ratio (SHR TR). The axial spacing to height ratio must not exceed the
maximum spacing to height ratio. The transverse spacing must not exceed the
maximum transverse spacing (SHR MAX TR). Additionally the product of the two
spacings should not exceed (SHR MAX)2.
SHR AX SHR TR ≤ (SHR MAX)2
Also check that the spacing is close to SHR NOM
(SHR AX SHR TR )0.5 = (SHR NOM) +/- 0.5
– If the spacing to height ratio is not acceptable then the lighting design
process must be iterated.

24. Daylighting
• The power consumption of a lighting system can be made responsive if the
control (switching) of the lighting system takes account of the fact that
daylight can make a contribution to the lighting of a room. A key variable in
the determination of daylight contribution to a room is the limiting depth of
the daylight into the room.
D
H
ρ s

25. Daylighting
• This depth determines the depth to which daylight can penetrate into a room and
make a contribution to lighting levels. The formula for limiting depth, D (m), is as
follows:
D is the limiting depth;
H is the height of the window header above floor level;
W is the width of the room parallel to the window;
ρs is the average surface reflectance of surfaces in the half of the room remote from
the window.
)
1
)(
(
2
s
W
H
H
W
D






26. Lighting Control
• The penetration depth can
be used to decide the
design of the switching
system for a lighting
system.
manual switching bank w/
timer control
photo sensor
D
occupancy sensor