The document discusses design considerations for lighting systems across various settings, emphasizing the need for adequate illumination, uniformity, color, and avoidance of glare. It details factors such as mounting height, lamp selection, and the effects of room characteristics on light distribution, as well as methods for calculating illumination levels. Additionally, it addresses strategies to minimize glare and enhance visual comfort in different environments, including homes, offices, stores, and industrial spaces.

1. MODULE 4
•Design considerations
• Preparation of lighting & electrical scheme
• Floodlighting Problems

2.  The purpose of lighting scheme is that it should provide good lighting, give proper
illumination, have absence of glare .
 It depends on the kind of occupancy, type of lighting fixtures, arrangement of fittings , size
of the room , number of fittings used etc.
 Every lighting installation should serve a specific purpose.
 In the home ,lighting system should facilitate domestic activities. Decorative arrangement
can also be selected to make the interior attractive.
 In store or shop , lighting depends on the goods that are stored .
 In factory , lighting arrangements are planned to increase productivity and improve the
quality of production. Safety should be given importance.
 In offices ,glare should be minimum.
 In hospitals, good distribution of light is required .In operation theatres , minimum glare
should be taken into consideration. In case of failure of supply , alternative arrangements
should be immediately available.
Lighting system considerations for different occupancies

3. The lighting scheme should be such that it may,
 Provide adequate illumination,
 Provide light distribution all over the working plane as uniform as possible,
 Provide light of suitable colour and
 Avoid glare and hard shadows as far as possible.
Design considerations of a good lighting scheme

4. In designing good lighting scheme , we have to consider mainly
 Illumination level
 Uniformity of illumination
 Colour of light
 Shadows
 Glare
 Mounting height
 Selection of required lamp and fitting & their spacing
 Size of the room
 Colour of surrounding walls
Design considerations of a good lighting scheme

5. Illumination Level : Intensity of illumination required for different types of work differ. For each
type of work there is a range of brightness most favorable to output i.e which causes minimum
fatigue and gives maximum output in terms of quality and quantity
Table shows the recommended intensity of illumination for different types of work.
Uniformity of Illumination: The human eye adjusts itself automatically to the brightness within
the field of vision. If there is a lack of uniformity, pupil or iris of the eye has to adjust more
frequently and thus fatigue is caused to the eye and productivity is reduced. Local lighting without
using matching general lighting creates psychological feelings of loneliness, gloom and
unfriendliness.
Color of the Light: The appearance of the body color entirely depends up on the color of the
incident light. In general composition of the light should be such that the color appears natural.
Day light fluorescent tubes now a day make it possible to illuminate economically even large
spaces with artificial day light giving good color rending and at sufficiently high level.
Design considerations of a good lighting scheme

6. Design considerations of a good lighting scheme

7. Shadows: A certain amount of shadows is desirable in artificial lighting as it helps to give shape
to the solid objects and makes them easily recognized.
Glare: It may be direct (or) reflected. Direct glare from a source of light is the more common, and
is more often a hindrance to vision. A glance at the sun proves that an extremely bright light
source causes acute eye discomfort
Mounting Height: In the case of direct lighting in the rooms of large floor area, the luminaries
should be mounted as close to the ceiling as possible. In the case of indirect lighting it would of
course be desirable to suspend luminaries far enough down from the ceiling in order to give
reasonably uniform on the ceiling.
Spacing of Luminaries: Correct spacing is one of great importance to provide uniform
illumination over the whole area and thus do away with comparatively dark areas which are so
often when the fittings are badly spaced.
Design considerations of a good lighting scheme

8. Selection of luminaries – A luminaire is the apparatus which distributes , filters , transforms the
light given by a lamp. Selection of lamps for different types of occupancies differ.
 For small premises tubular fluorescent lamps or tungsten filament lamps can be used .
 In large premises , lighting can be carried out by using high intensity sources such as
mercury or sodium discharge lamps. Depending on the type of illumination required ,
(direct , indirect etc ) reflector types can be selected
Size of the room – The lumen output of the sources is not fully utilized at the work place. Part of
it is lost in the fittings , part is directed to walls and ceilings where part will be absorbed and part
will be reflected. This is taken into account by a factor called coefficient of utilization. Coefficient
of utilization depends on the lumen output of the fitting , size and shape of the room , reflection
factors of wall , ceiling , height of the ceiling , arrangement of fittings etc.
Color of Surrounding Walls: The illumination in any room depends upon the light reflected from
the walls and ceilings. White walls and ceilings reflect more light as compared to colored ones.
Design considerations of a good lighting scheme

9. • Mounting heights and spacing of fittings : Distance of light source from the wall should be
equal to one half the distance between 2 adjacent light sources. Also distance between light
fittings should not exceed 1.5 times the mounting height.
• Conditions of use : In different types of installations , conditions of use of light fittings vary .
Dust and dirt of the surroundings may get deposited on the light fittings and hence deteriorate
the lamp efficiency.
If regular periodic cleaning and assuming good atmospheric conditions , the value of
maintenance factor may be taken as 0.8.
But for dusty atmospheres, the factor may be assumed as 0.4.
Depreciation factor = 1/(maintenance factor)
Design considerations of a good lighting scheme

10. Basic Design technique-
• Determination of Quantity
– Point by point method (Inverse Square law & Lambert’s Cosine law)
– Lumen method
– Light loss factor (LLF) or Maintenance factor (M.F.)
• Determination of Quality
– Visual Comfort Probability
– Glare
Methods of lighting calculations

11. 1. WATTS PER SQUARE METER METHOD
This is principally the rule of thumb method. Very handy for rough calculations and checking.
It consists of making an allowance of Watts/sqm of area to be illuminated according to the
illumination desired on the assumption of an average figure of overall efficiency of the
system.
(Eg - Suppose u have a 15x6m hall , to be illuminated .
Area of the hall = 15x6=90sqm.
Assume 10 watt/sqm as the illumination requirement. So we require 900Watts.
That means, if you are using 60W lamps , then we require 15 lamps.)
Methods of lighting calculations

12. 2. LUMEN METHOD
This method is applicable in cases where the sources of light are such as to produce an
approximate uniform illumination over the working plane.
Lumen on working plane = No.of lamps x wattage of each lamp x efficiency of each lamp in
terms of lumens/watt x coeff of utilisation x maintenance factor.
3. POINT TO POINT METHOD
this method is applicable where illumination at a point due to one or more sources of light
is required. If 2 and more than 2 lamps are illuminating the same working plane , then
illumination due to each can be calculated and added. This method is adopted in some special
cases like flood lighting and yard lighting.
Methods of lighting calculations

13. • Depreciation factor – ratio of net illumination output after a certain gap of time to
illumination output under normal condition of new installation.
– Light emitted by source reduces due to dust or dust decomposition on light
– So quantity of light reflected also get reduced.
– This reduction of light can be minimized by cleaning the light fittings or white washing.
– But absolute cleanliness is not possible hence we need to consider depreciation factor.
This is also known as soiling factor or loss factor. This is not only due to evaporation of
filament material and reflector coating but due to fluctuation of voltage also.
• Maintenance factor – is the reciprocal of depreciation factor. It dependent on soiling effect
and also on the cleaning schedule.
The illumination produced by a light source decreases due to ageing and accumulation of
dust on the lamp surface, reflectors, etc.
MF = Illumination under normal working condition / Illumination when everything is clean
MF = 1/ DF (Depreciation factor)
Methods of lighting calculations

14. Absorption factor – In case of places having smoke, steam, dust, fumes, fogs etc , light flux
emitted is partially absorbed by these contaminations present in the air.
Absorption factor for various types of atmospheres
For clean atmosphere = 1
Fog laden atmosphere = 0.75
Steam / fume/ contaminated atmosphere in factories = 0.5
Reflection factor – is the ratio of reflected luminous flux to total incidental luminous flux.
Ceiling reflection factor values
70% for very light colours and white
50% for light colours
30% for medium shades
Wall reflection factor values
50% for very light colours and white
10% for light colours
30% for medium shades
Methods of lighting calculations

15. • Coefficient of Utilization ( Utilization factor)
All light flux emitted by a lamp or luminaire does not reach surface or working plane being
illuminated.A major portion of light output goes to the wall and ceiling and will be reflected
back to the working plane.
 The ratio of effective luminous flux reaching working table to total luminous flux emitted is
known as utilization factor or coefficient of utilization
 Direct fixture or downlight – CU = .85
 Indirect fixture – CU = .50
 Spot or Accent – CU = .95
 Ambient or Wash – CU =.75
Methods of lighting calculations

16. Tables for Utilization factor for various room indexes and reflection factors of ceiling/wall/floor
are available .
Room Index :
Room Index for a rectangular area is given by
• Kf = LW/(L+W)hm
L- overall length of room
W – overall width
hm-mounting height of fittings above working plane.
Methods of lighting calculations

17. Light Loss Factor (LLF)
 Light loss due to deteriorating lamps
 It is the product of several factors, each depreciating light output at certain point in time
in the future compared to initial light output.
 LLF has mainly 2 components:
i. LLD (Lamp lumen depreciation ):
This recognizes the fact that lumen output depreciates over time
ii. LDD (Luminaire Dirt Depreciation):
The greatest loss of light output is due to the dirt accumulation on lamps and luminaire
reflecting surface
∴ LLF = LLD x LDD
• Industry standard of .85 for a light loss factor
Typical LLF values
Air conditioned office - 0.8
Clean Industrial - 0.7
Dirty Industrial - 0.6
Methods of lighting calculations

18. Calculation of illumination levels in interiors
The emperical formula to calculate the illumination is
where N = no. of fittings needed.
E= required illumination(lux)
A-working area (sqm)
O-luminous flux produced per lamp(lumens)
Cu-coefficient of utilization
MF- maintenance factor.
Methods of lighting calculations
Total Wattage of fixtures
= No: of lamps * watt of each lamp
Efficacy or Efficiency= Lumens /
Watt

19. • A small assembly shop 15m long , 9m wide and 3m upto the trusses is to be illuminated to a
level of 200 lux. The coefficient of utilisation is 0.75and maintenance factor is 0.8. Calculate
the no. of lamps , required to illuminate the whole area if the lumen output selected is
3000lumens.
Working Area , A = 15m x 9m
Required Illumination , E = 200 lux
Lumen output of one lamp ,O = 3000 lumens
Coefficient of utilization , CU = 0.75
Maintenance Factor , MF = 0.8
Number of lamps required , N = (EA)/(OxCUxMF)
= (200x15x9)/(3000x0.75x0.8)
= 15
Methods of lighting calculations

20. • An office 30m x 15m is illuminated by 40W fluorescent lamps of lumen output 2700
lumens.the average illumination required at the work place is 200lux.Calculate the number of
lamps required to be fitted in the office. Assume coefficient of utilization to be 0.6 and
depreciation factor 1.25.
Working Area , A = 30m x 15m
Required Illumination , E = 200 lux
Lumen output of one lamp ,O = 2700 lumens
Coefficient of utilisation , CU = 0.6
Maintenance Factor , MF = 1/DF = 1/1.25 = 0.8
Number of lamps required , N = (EA)/(OxCUxMF)
= (200x30x15)/(2700x0.6x0.8)
= 70
Methods of lighting calculations

21. • A workshop measure 10m x 25m. The shop is illuminated by 24 lamps of 200 W each. The
lumen efficiency of each lamp is 15lumens/Watt. Maintenance factor is 0.8 and coefficient of
utilization is 0.5Determine the illumination on the working plane.
A = 10m x 25m
Total lumens given by the lamps = No.of lamps x wattage of each lamp x luminous
efficiency of each lamp
= 24x200x15 = 72000lumens
N = (EA)/(OxCUxMF)
E= 24x200x15x0.5x0.8/10x25 = 28800/250 = 115 lux
Methods of lighting calculations

22. Luminous flux Table of different types of light sources.
Methods of lighting calculations

23. Luminous flux Table of different types of light sources.
Methods of lighting calculations

24. Basic Design technique-
• Determination of Quantity
– Point by point method
– Lumen method
– Light loss factor (LLF) or Maintenance factor (M.F.)
• Determination of Quality
– Visual Comfort Probability
– Glare
– CRI
Methods of lighting calculations

25. Quality of Illumination
Three quality issues are addressed in this section.
•glare
•uniformity of illuminance
•color rendition
Glare
 Glare is a sensation caused by luminances in the visual field that are too bright. Discomfort,
annoyance, or reduced productivity can result.
 A bright object alone does not necessarily cause glare, but a bright object in front of a dark
background, however, usually will cause glare.
 Contrast is the relationship between the luminance of an object and its background. Although the
visual task generally becomes easier with increased contrast, too much contrast causes glare and
makes the visual task much more difficult.
Methods of lighting calculations

26. VCP
 You can reduce glare or luminance ratios by not exceeding suggested light levels and by using
lighting equipment designed to reduce glare.
 A louver or lens is commonly used to block direct viewing of a light source. Indirect lighting, or
uplighting, can create a low glare environment by uniformly lighting the ceiling. Also, proper fixture
placement can reduce reflected glare on work surfaces or computer screens.
 Standard data now provided with luminaire specifications include tables of its visual comfort
probability (VCP) ratings for various room geometries.
 Visual comfort probability (VCP) indicates the percent of people who are comfortable with the
glare from a fixture.
 The VCP index provides an indication of the percentage of people in a given space that would find
the glare from a fixture to be acceptable.
 A minimum VCP of 70 is recommended for commercial interiors, while luminaires with VCPs
exceeding 80 are recommended in computer areas.
Methods of lighting calculations

27. Uniformity of Illuminance on Tasks
 The uniformity of illuminance is a quality issue that addresses how evenly light spreads over a
task area. Although a room's average illuminance may be appropriate, two factors may
compromise uniformity.
 Improper fixture placement based on the luminaire's spacing criteria (ratio of maxim
recommended fixture spacing distance to mounting height above task height)
 Fixtures that are retrofit with reflectors that narrow the light distribution
Non-uniform illuminance causes several problems:
• Inadequate light levels in some areas
• Visual discomfort when tasks require frequent shifting of view from underlit to overlit areas
• Bright spots and patches of light on floors and walls that cause distraction and generate a low
quality appearance
Methods of lighting calculations

28. Color Rendition
 The ability to see colors properly is another aspect of lighting quality.
 Light sources vary in their ability to accurately reflect the true colors of people and objects.
 The color rendering index (CRI) scale is used to compare the effect of a light source on the
color appearance of its surroundings.
 A scale of 0 to 100 defines the CRI.
 A higher CRI means better color rendering, or less color shift.
 CRIs in the range of 75-100 are considered excellent, while 65-75 are good. The range of 55-65
is fair, and 0-55 is poor.
 Under higher CRI sources, surface colors appear brighter, improving the aesthetics of the space.
Sometimes, higher CRI sources create the illusion of higher illuminance levels.
Methods of lighting calculations

29.  Headlights of oncoming traffic – direct glare
 Headlights in rear view mirror when driving at night – indirect glare
Direct & Indirect Glare
Methods of lighting calculations

30. Direct & Indirect Glare Zones
 The direct glare zone is between 45°and 90°
 The indirect glare zone is between 0° and 45°
Methods of lighting calculations

31. Methods of lighting calculations

32. Strategies for Reducing Unwanted Glare
Strategies commonly employed to reduce unwanted levels of glare include:
• Indirect lighting that throws more light upward than downward, diffusing the light and reducing
glare on computer screens
• Parabolic louvers, special lenses or other diffusing media on fixtures that diffuse the fixture's
light output
• In an office, it may be possible to de-emphasize the ambient lighting system with reduced light
output and diffusing media, while providing adjustable task fixtures at workstations
• Relocating the light source
• Relocating the task or changing its orientation until the glare is removed
Methods of lighting calculations

33. Strategies for Reducing Unwanted Glare
• Changing the surface reflectance of the task
• Use blinds or shades on windows to control the amount or transmittance angle of sunlight
entering the space
• You can reduce glare or luminance ratios by not exceeding suggested light levels and by using
lighting equipment designed to reduce glare.
• A louver or lens is commonly used to block direct viewing of a light source.
• Indirect lighting, or uplighting, can create a low glare environment by uniformly lighting the
ceiling.
• Also, proper fixture placement can reduce reflected glare on work surfaces or computer screens.
Methods of lighting calculations

34. 10 Ways to Reduce Glare
Glare is controlled by adjusting the light source or the surface reflecting it and by filtering light
before it reaches the eyes. The following solutions seek to control glare in these ways.
• Filter & diffuse light. Use filtered light instead of direct light, which causes the most glare.
Diffuse light with lamp shades or globes, and use adjustable curtains or blinds on windows.
• Adjust work areas. Make sure work surfaces have a dull or matte finish since shiny surfaces
reflect light more. Even adjusting colors on walls and ceilings can add contrast and reduce glare
in work areas.
• Wear polarized lenses. Polarized glasses reduce glare in situations where bright light reflects off
a shiny surface like water, snow, glossy printed paper or painted surfaces.
• Look for anti-glare coatings. Anti-glare treatment can reduce glare at night and inside from
computer screens and inside light. Ask your ophthalmologist for the coating for prescription
eyewear or purchase anti-glare safety glasses.
Methods of lighting calculations

35. • Adjust light level. Although light level does impact visual performance, it’s not always brighter
light levels that are needed. Often, raising the overall light level can help with contrast and thus
visibility.
• Add a desk lamp. In some situations, adding a desk lamp for viewing paper documents helps
significantly by illuminating the document while avoiding excessive light on the computer
screen. Just make sure the lamp doesn’t cause additional glare off a computer monitor.
• Use adjustable lighting. Make sure light is adjustable for dimness or brightness to suit the
situation.
• Let technology help. Use computer monitors with adjustable contrast settings, and change the
background color on the computer screen to suit the lighting situation.
• Consider placement of computers. Adjust the angle and placement of monitors to reduce glare
from overhead lights. Ideally, place them at a right angle to all lighting sources, including
windows.
• Try foam seals & wrap-around glasses. Safety glasses with foam padding and wrap-around
sunglasses and safety glasses help protect from side/angular glare, which can cause as much
damage as direct sunlight
Methods of lighting calculations

36. • Flood lighting Calculations
While calculating the number of projectors required for the flood lighting, it is necessary to know
the level of illumination required
Illumination level required – The illumination level in lux (lm/sqm) required depends on the type
of the building, purpose of flood lighting, amount of reflecting light in the vicinity etc.
Waste light factor – When several projectors are illuminating a surface there is bound to be a
certain amount of overlap and also some of the light will fall beyond the area to be illuminated
. These 2 effects are taken into account by multiplying the theoretical lumens by waste light
factor .This is generally taken as 1.2 for rectangular areas and 1.5 for irregular objects like
statues.
Depreciation factor – Ratio of illumination under ideal condition to the illumination under normal
condition. This depreciation is due to the dust and dirt accumulated on the reflector surfaces.
Coefficient of utilisation – Also called the beam factor , is defined as the ratio of beam lumen to
lamp lumen.Its value lies between 0.3 and 0.5
Flood Lighting system

37. Number of projectors-
N=(A x E x DF x Waste light factor)/( CU x wattage of the lamp x luminous
efficiency of the lamps
N- no.of projectors
A- Area of surface to be illuminated in sqm
E-illumination level required in lm/sqm
Gross lumen required from lamps
= A x E x Waste light factor x DF / CU
Flood Lighting system

38. • The front of a building 45m x 20m is illuminated by 20 , 1000W lamps
arranged so that uniform illumination on the surface is obtained. Assuming a
luminous efficiency of 18 lumens/Watt, CU = 0.4 , waste light factor 1.2, DF –
1.3,Determine the illumination on the surface.
N=(A x E x DF x Waste light factor)/( CU x wattage of the lamp x luminous
efficiency of the lamps
20 = 45 x 20 x E x 1.3x 1.2/ 0.4 x 1000 x 18
E = 0.4 x 1000 x 18 x 20 /900 x 1.3 x 1.2 = 102.56 lux
Flood Lighting system

39. It is desired to illuminate a drawing hall with an average illumination of 200lux.The hall is
30×20m2 .The lamps are to be fitted 4m from ground floor. Find the number of lamps and
wattage / lamp for the lighting scheme .Given efficiency of the lamps and available as 25
lumens/watt, depreciation factor 0.8 and coefficient of utilization 0.75, space height ratio
between 0.8 and 1.2 .Give satisfactory spacing arrangement.
Submission date: December 11th
Assignment 2