1. AR 4.5
BUILDING SERVICES - II:
ELECTRICAL SERVICES:
Unit – V:
Lighting Calculation:
NBC standards, nominal
illumination
levels
in
building
interiors, lux, lumen, intensity, lighting schemes.

2. ILLUMINATION AND LUX:
What is the method for calculating illumination ?
The problem of the Architect / Lighting Designer at the
functional level is to determine how many lights and
where to place them to get the correct level of illumination
for a given activity.
What do we understand by LUX ?
The lux (symbol: lx) is the SI unit of illuminance and
luminous emittance, measuring luminous flux per unit
area. It is used in photometry as a measure of the
intensity, as perceived by the human eye, of light that hits
or passes through a surface. It is analogous to the
radiometric unit watts per square metre, but with the
power at each wavelength weighted according to the
luminosity function, a standardized model of human
visual brightness perception. In English, "lux" is used in
both singular and plural.

3. ILLUMINATION AND LUX:
One lux is equal to one lumen per square metre:
A lux meter for measuring illuminances in work places.

4. ILLUMINATION AND LUX:
One lux is equal to one lumen per square metre:
In other words ..
LUX =
Level of Illumination.
OR
LUX (lx)
=
Lumens / Sq.M.
Level of Illumination ?
LUMEN METHOD:
This method works perfectly in most cases where the
height of the ceiling is within 3000 mm from floor
level, the Working Plane is between 750 to 1000 mm and
proportions of the area are proper.

5. ILLUMINATION AND LUX:
How To Calculate Lux ?
How do I calculate lux - the formula?
Lux level = total light output (lumens) / area (square
meters)
Total Light Output = lumens per fixture * number of
fixtures
Therefore
Number of Fixtures = (Lux level * area) / lumens per
fixture

6. ILLUMINATION AND LUX:
Every Lamp has certain Lumens.
You need to look up the manufacturer data for your light
fitting to get the lumens per fixture.
S.No.
1.
2.
3.
Type of Lamp.
36 W Tube Light.
60 W GLS Lamp.
10 W CFL.
Lumens Output.
2400 Lumens.
600 Lumens.
600 Lumens.

7. ILLUMINATION AND LUX:
Example:
Assume a Room size of = 10000 x 8000 x 3000 = 80 Sq.M.
Area =
80 Sq.M.
Suppose the desired lux level or Illumination = 300 lx.
Total Lumens required = 300 x 80 = 24,000 lumens.
Assuming that you are using 36W Lamp (FTL) and the
same has 2,400 lumens illumination.
Number of Fixtures required = 24,000 / 2400 = 10 Nos.
So you need 10 Nos. of 36W Tube Light Fittings.

8. ILLUMINATION AND LUX:
What we did above is still not sufficient as there are
certain Correction Factors involved. There are basically
two Correction Factors i.e., Utilization Factor = UF and
Maintenance Factor = MF.
UTILIZATION FACTOR: (UF)
This may be due different
Reflectance's, Dimensions etc.,
reasons
viz.,
Room
The utilization factor (UF) is a Direct ratio. This is the
proportion of the downward luminous flux that reaches
the work area directly without reflection. It depends on
the shape of the room. The Direct ratio has a low value
with a tall narrow room (small RI) and a high value for a
wide room (large RI).

9. ILLUMINATION AND LUX:
The light distribution from the luminaries. Luminaries
that emit light through a larger solid angle will generally
have a smaller direct ratio that luminaries that emit light
in a narrower beam.
There exist data sheets of UF for rooms of different shapes
and luminaries of a common type.
Catalogues of luminaries often provide data sheets of UF
for rooms.
Normally we take 0.8 as the Utilization Factor.

10. ILLUMINATION AND LUX:
This utilization factor is somewhat more complicated to
determine than the maintenance factor.
The utilization factor will depend on the following:
The luminarie properties. One needs the light output ratio
(LOR). How much of the light emitted by the lamps
actually leaves the luminarie? An enclosed lamp in a
luminarie with low reflectivity will have a smaller LOR
than a naked lamp.
The light emitted downwards will probably reach the
work area without reflections. However light emitted
upwards can only reach the work area after reflection(s)
from surfaces.

11. ILLUMINATION AND LUX:
The utilization factor will depend on the following:
The reflectance of the room surfaces. Are the surfaces
(walls, ceiling) light or dark in color?
(A color with strong chroma does not reflect other colors).
Reflectance's are available from manufacturers of paints
and furniture finishing's.
It is usual to make the reflectance of the ceiling highest,
walls slightly lower and the floor darker.
Reflectance's of desks should be 20-40%. Do not choose
very dark wood, or bright surfaces.
The geometric proportion of the room. The geometric
shape of the room will affect the UF. A factor called the
room index (RI) is defined from the horizontal vertical
areas of the room.

12. ILLUMINATION AND LUX:
MAINTENANCE FACTOR: (MF)
It is also known as LLF OR Light Loss Factor. This may be
due different reasons viz., Time, Temperature, Cleanliness
etc.,
The maintenance factor gives an estimate of how lighting
conditions will deteriorate through use.
Some factors are:
• Dust and dirt inside luminaries surfaces.
• Aging of light bulbs emitting less light.
• Cleaning of room surfaces, e.g. ceiling.
Normally we take 0.75 to 0.8 as the Maintenance Factor.

13. ILLUMINATION AND LUX:
Coming back to our earlier Example where we said that
we need 10 Nos. of 36W Tube Light Fittings.
Now with application of UF and MF it will be as follows:
No. of Fixtures = 10 / 0.8 x 0.8 = 15.625 i.e., 16 Nos.
But practically many times to maintain the balance we
may use upto 12 Nos. of fixtures also.
Formula
for
Number of
Fixtures.
Lux x Area /
Lumen
Output x MF
x UF
300 x 80 /
2400 x 0.8 x 0.8
15.625

14. LIMITATION OF LUMEN METHOD:
There are certain limitations to this method, but all said
and done this works perfectly for 90% of the installations
where the parameters are within the limits.
Height is not considered.
Fixtures or luminaries changes are not considered. (Polar
curve etc.,)
Room Reflectance's are not considered.
It does not distinguish between different fixture behaviors
i.e., point source or linear source etc.,
For this there is one more complicated method known as
POIINT BY POINT METHOD. This is more specific for
experts in Lighting Design and detailing.

15. GLARE:
The control of glare:
Glare occurs in both natural (daylight) and in interior
lighting situations. It is most annoying in the interior light
environment where the lighting is under human control.
The glare annoyance depends on a number of factors
In a supermarket people are on the move and not always
looking in same direction.
In a classroom students are usually looking in a fixed
direction.
In a classroom, students are reading, this is a moderately
difficult visual task.
Students are fixed for a long period of time.
Standards for glare depend on the use of the visual
environment.

16. GLARE:
The glare index
There is quantity called the discomfort glare constant (g)
which is:
Glare index.
0 - 10
10 - 16
16 - 22
22 – 28
Reaction.
Imperceptible
Noticeable
Acceptable
Uncomfortable
> 28
Intolerable

17. GLARE:
More visually demanding tasks with high illuminance
levels are less tolerant of glare.
Limiting Occupations
GI
16
Drawing offices, very fine visual inspections.
Offices, libraries, keyboard and VDT work
19
(reflections from screen).
22
25
28
Kitchen, reception area, fine assembly.
Stock rooms, assembly line for easy tasks.
Indoor car park, rough industrial work.
(At present time, do not require you to calculate the glare
index, require you to know what it is and when it is most
important to eliminate.)

18. GLARE:
CONTROL OF GLARE:
First of all, glare from all sources is additive and people
get annoyed by all sources of discomfort glare.
Obviously, cutting down the illuminance of the glare
source, Ls is a good idea. This does not mean reducing the
light level in the room. The higher the illumination of the
background, the smaller the glare constant. So rather than
having one very bright luminaire, have a number of
dimmer luminaries.
Most of the visual tasks involve looking horizontally or
slightly down. So keep luminaries out of the low angle
vision. So do not gives walls too high a reflectance. Do not
give the floors too high reflectance (no glossy light floors!).

19. GLARE:
TIPS TO CONTROL GLARE:
Keep luminance of source down. Use of diffusers and
louvres. Cutting down glare also cuts down total light
emitted and this problem also needs to be tackled.
Reflected light can also be a source of glare.
Keep luminaires out of field of view. High ceilings are good.
Keep area of source small.
To cut down glare, avoid luminaires that emit light to
sides (e.g. battern luminaire with a diffuser at the
sides), light emitted more in downward direction avoids
visual discomfort.

20. GLARE:
UPLIGHTING:
In this form of lighting, lighting is directed upwards to the
ceiling. Reflected light from the ceiling provides the
general illumination in the room.
Advantages, elimination of glare is one of the major
advantages.
Re-introduction driven by the increasing use of
computers.
Disadvantage, it is somewhat inefficient. Low conversion
of electrical energy into usable light.
If the Ceiling is quite bright, it will have less visual
emphasis on other areas of room, furniture, floors.
To get an even illumination on the ceiling requires that
you have a high ceiling.

21. GLARE:
UPLIGHTING:
You either like it or not. It is possible to use combinations
of direct diffuse and indirect lighting.
Illumination can be calculated using lumen method in
conjunction with transfer function tables.
Need to maintain a uniform illumination on ceiling.
Eliminates light hot-spots that can result in glare.
Harder with low ceiling.
Besides less glare, concentrated beam downlights result in
darker ceiling. This can result in an oppressive
psychological effect.

22. LIGHTING STANDARDS:
What are the legal requirements for office lighting? Is
there a legal requirement for daylight?
The only legal requirements are 'sufficient and suitable'
and similar wording in health and safety legislation. There
is no absolute legal requirement for daylight, but it is a
requirement that it be provided if practicable. Various
guidance documents suggest good practice, but are not
themselves mandatory.
What is the recommended lighting level for offices?
The Code for Lighting recommends a maintained
illuminance of 500 lux for general offices (e.g. writing,
typing, reading, data processing, etc.) and for CAD work
stations and conference/meetings rooms. Where the main
task is less demanding, e.g. filing, a lower level of 300 lux
is recommended.

23. ILLUMINATION LEVELS AND LIMITING GLARE:
The table following lists illumination levels suitable for a
range of situations: the quality of these levels could be
influenced by glare and an acceptable limiting index is
also shown. The glare index is calculated by considering
the light source location, the luminances of the source, the
effect of surroundings and the size of the source.
Glare indices for artificial light range from about 10 for a
shaded light fitting having low output to about 30 for an
un shaded lamp.

24. ILLUMINATION LEVELS AND LIMITING GLARE:
As seen from this illustration, various basic decisions have
to be made concerning lighting objectives and whether the
system involves daylight, electric light or a combined
system. With electric or combined systems, further
decisions must be taken concerning the way light is
distributed by particular fittings, and upon their positions
relative to each other as well as in relation to the surface to
be illuminated. As with day lighting, light-coloured and
highly reflective room surfaces help to provide more
illumination from the same amount of energy source – it
preserves the luminance effect of the light source.

25. ILLUMINATION LEVELS AND LIMITING GLARE:
Location.
Illuminance. (lx)
Limiting Glare Index.
Entrance Hall.
150
22
Staircase.
150
22
Corridors.
100
22
Outdoor Entrances.
30
22
Casual Assembly Work.
200
25
Rough / Heavy Work.
300
28
Medium Assembly Work.
500
25
Fine Assembly Work.
1,000
22
Precision Work.
1,500
16
General Office Work.
500
19
Computer Room.
750
16
Drawing Office.
750
16
Filing Room.
300
22
Shop Counter.
500
22
Super Market.
500
22

26. ILLUMINATION LEVELS AND LIMITING GLARE:
Location.
Illuminance. (lx)
Limiting Glare Index.
Class Room.
300
16
Laboratory.
500
16
Public House Bar.
150
22
Restaurant.
100
22
Kitchen.
500
22
Living Room.
50
NA.
Reading Room.
150
NA.
Study Room.
300
NA.
Kitchen.
300
NA.
Bed Room.
50
NA.
Hall.
150
NA.
Library – Reading Area.
200
19
Library – Tables.
600
16
Library – Counter.
600
16
Dwellings:

27. LIGHTING LEVELS:
(lx)
Activity.
100 Casual seeing
300
500
750
1000
1500
2000
Corridors, changing rooms, stores
Loading bays, switch rooms, plant
rooms
Continuously occupied
Foyers, entrance halls, dining rooms
Libraries, sports halls, lecture
Visual tasks moderately easy
theatres.
General
offices,
kitchens,
Visual tasks moderately difficult
laboratories, retail shops.
Drawing offices, meat inspection,
Visual tasks difficult
chain stores.
General
inspection,
electronic
Visual tasks very difficult
assembly, paint work, super
markets.
Fine work and inspection, precision
Visual tasks extremely difficult
assembly.
Visual tasks exceptionally
Assembly of minute items, finished
difficult
fabric inspection.
150 Some perception of detail
200
Area.

28. ELECTRICAL FORMULAS:
Demand for Power (kW) = System Input Wattage (W) ÷
1,000
Energy Consumption (kWh) = System Input Wattage (kW)
x Hours of Operation/Year
Hours of Operation / Year = Operating Hours / Day x
Operating Days / Week x Operating Weeks / Year
Lighting System Efficacy (Lumens per Watt or LPW) =
System Lumen Output ÷ Input Wattage
Unit Power Density (W/ Sq.M.) = Total System Input

29. ELECTRICAL FORMULAS:
Wattage (W) ÷ Total Area (Sq. m.)
Watts (W) = Volts (V) x Current in Amperes (A) x Power
Factor (PF)
Voltage (V) = Current in Amperes (A) x Impedance
(Ohms) [Ohm's Law]

30. ECONOMIC FORMULAS:
Simple Payback on an Investment (Years) = Net
Installation Cost ÷ Annual Energy Savings.
5-Year Cash Flow = 5 Years - Payback (Years) x Annual
Energy Savings.
Simple Return on Investment (%) = [Annual Energy
Savings ÷ Net Installation Cost ] x 100

31. DESIGN FORMULAS:
Footcandles & Lumens
Footcandles (fc) = Total Lumens (lm) ÷ Area in Square Feet
1 Lux (lx) = 1 Footcandle (fc) x 10.76
Lux = Total Lumens ÷ Area in Square Meters

32. SUNLIGHT:
400 lux:
Sunrise or sunset on a clear day.
1,000 lux:
Overcast day.
10,000–25,000 lux:
Full daylight (not direct sun)
32,000–130,000 lux: Direct sunlight.