1. LUMEN METHOD OF LIGHTING DESIGN:
Lumen method of design is the most widely used for the determination
of lighting layout for providing illumination on the working plane from
overhead lamps arranged in a regular pattern.
โขThis method is based on the concept of Utilisation factor.
Utilisation factor = ratio of the total flux received on the working plane
(Fr) to the total flux emitted by all the lamps (Fl).
For example , if all lamps together emit 10 000 lumen and a plane 0.8 m
high over the whole of the room receives 5000 lumen.
Utilisation factor = Fr = 5 000 = 0.5
Fl 10 000
UF
โขFor downward direct lighting 0.4 to 0.9
โขFor diffusing fittings 0.2 to 0.5
โขFor indirect lighting 0.05 to 0.2
2. LUMEN METHOD OF LIGHTING DESIGN:
Maintenance factor: a further allowance should be made for dirt on
the fitting or deterioration of lamp output. UF should be multiplied by
maintenance factor (MF) . It is usually taken as 0.8.
Illumination is the flux received divided by the area (A). If the room is
50 mยฒ, then illumination is :
E = 5000 = 100 lux (lumen/mยฒ)
50
1. If we know the lampsโ output, we can calculate the illumination:
E = F X UF X MF where, F = lampsโ output
A E = Illumination
UF= Utilization factor
MF = Maintenance factor
3. LUMEN METHOD OF LIGHTING DESIGN:
2. If we know what illumination we want to get, we can find the lamp
output necessary to achieve this:
F = A X E
UF X MF
So this method can be used either as a checking tool or directly as a
design tool.
4. LUMEN METHOD OF LIGHTING DESIGN:
Problem 1: An office 10m X 5m requires an illumination level of 300
lux on the working plane. It is proposed to use 40 watt fluorescent
fittings having a rated output of 2440 lumens each. Design the lighting
scheme.
E = Lux on working plane = 300 lux
A = Floor area = 10m X 5m
F = total lampsโ output = n X 2440 lumens
where, n = number of lamps
Now, using the formula,
F = A X E
UF X MF
n X 2440 = 10 X 5 X 300 , n = 15.39
0.5 X 0.8
So we may use 15 /16 fittings of 40 watt fluorescent lamps.
5. LUMEN METHOD OF LIGHTING DESIGN:
Problem 2: Consider a private office of 150 sq. ft. area. We wish to
use a specific lamp that has 2440 lumens to achieve 40 fc.
E = on working plane = 40 foot candle
A = Floor area = 150 sq. ft.
F = total lampsโ output = n X 2440
where, n = number of lamps
Now, using the formula,
F = A X E
UF X MF
n X 2440 = 150 X 40 = 6.14
0.5 X 0.8
So we may use 6 fittings of 40 watt fluorescent lamps.
We need, 6 nos. Single lamp luminaire
3 nos. 2 lamp luminaire
2 nos 3 lamp luminaire
1 no. 6 lamp luminaire
6. WATTS-PER-SQUARE FOOT METHOD:
โขMultiply room area in sq.ft. by watts/sq.ft. (refer table).
โขHow many watts of either fluorescent or halogen sources you need to
achieve.
Sl.
No.
Average light level desired
& typical application
Watt per square foot
fluorescent/ compact
fluorescent /HID lights
Watt per square foot of
incandescent / halogen
lamps
1 2.5 โ 5 fc (foot-candle)
Hotel corridors, stair
towers
0.1 โ 0.2 0.3 โ 0.7
2 5 โ 10 fc
Office corridors, parking
garages, theatres(house
lights)
0.2 โ 0.4 0.7 โ 1.0
3 10 โ 20 fc
Building lobbies, waiting
areas, elevator lobbies,
malls, hotel function
spaces, school corridors
0.4 โ 0.8 1.0 โ 2.0
7. WATTS-PER-SQUARE FOOT METHOD:
* These levels are for general lighting only. it is not good to produce high
light levels of general light using halogen sources. However we can use
halogen sources for accent lighting in these space types.
Sl.
No.
Average light level desired
& typical application
Watt per square foot
fluorescent, compact
fluorescent or HID lights
Watt per square foot of
incandescent or halogen
lamps
4 20 โ 50 fc
Office areas, classrooms,
lecture halls, conference
rooms, ambient retail
lighting, industrial
workshops, gyms
0.8 โ 1.2 Not recommended*
5 50 โ 100 fc
Grocery stores,
laboratories, work areas,
sports courts
1.2 โ 2.0 Not recommended*
8. WATTS-PER-SQUARE FOOT METHOD:
PROBLEM 1:
โขAverage overall proper light level for a class room is about 50 foot-
candle.
โขUsing table โ approximate amount of light needed = 1.2 watts/sq.ft. of
fluorescent lighting.
โขArea of classroom = 800 sq.ft.
โขTotal lighting power needed for this room = (800 X 1.2) watt = 960 watt.
โขIf we plan on using luminaires with 2-40 watt lamps:
We will need = 960 = 12 luminaires
40 X 2
โขIf we plan on using luminaires with two 32-watt lamps each:
We will need = 960 = 15 luminaires
32 X 2
9. WATTS-PER-SQUARE FOOT METHOD:
PROBLEM 2:
โขConsider the house lighting for a motion picture theater:
Recommended light level = 10 fc
โขLighting needs to dim over a full range โ hence choose halogen lighting.
โขUsing table โ approximate amount of light needed = 1.0 watts/sq.ft.
โขArea of theater hall = 3000 sq.ft.
โขTotal lighting power needed for this room=(3000X1.0) watt = 3000 watt.
โขIf we plan on using luminaires with 60 watt downlights:
We will need = 3000 = 50 luminaires
60
โขIf we plan on using luminaires with 100 watt downlights:
We will need = 3000 = 30 luminaires
100
