Incandescent Light Bulb

LUMEN DESIGN METHOD Where: N = E A F UF LLF N = number of lamps E = level of illuminance A = Area at working plane height F= Flux output of each lamp UF = Utilisation Factor LLF = Light Loss Factor N = E A F UF LLF From Guidance (eg CIBSE) Calculated Manufacturers’ literature By calculation or tables By calculation or tables

EXAMPLE A factory space measuring 40m by 12m by 4m in height requires a service illumination of 500 lux on the workbenches which are set 1m above the floor. The 65W tubular fluorescent lamps chosen have a luminous efficacy of 80lm/W. They are to be mounted on the ceiling in luminaires which have a DLOR of 50%. The room reflectances are 0.5 for the ceiling and 0.3 for the walls; the initial light loss factor is 0.7. Using the lumen design method to calculate the number of lamps required and suggest a suitable layout for the fittings.

E = 500 lux A = 40m x 12m = 480 m2 F = 65 W x 80 lm/W = 5200 lumens N = E A F UF LLF E = 500 lux A = 40m x 12m = 480 m2 F = 65 W x 80 lm/W = 5200 lumens LLF = 0.7 UF = (next slide…….)

UF First we need to calculate the Room Index (RI) RI = L W Hm (L + W) Where: L = length of room W = width of room Hm = mounting height of luminaire above working plane RI = 40 x 12 3 (40 + 12) RI = 3

0.46

E = 500 lux A = 40m x 12m = 480 m2 F = 65 W x 80 lm/W = 5200 lumens N = E A F UF LLF E = 500 lux A = 40m x 12m = 480 m2 F = 65 W x 80 lm/W = 5200 lumens LLF = 0.7 UF = 0.46 N = 500 x 480 5200 x 0.46 x 0.7 N = 144 lamps

144 lamps Suggested layout = 9 rows of 16 luminaires Check spacing using Smax = 1.5 x Hm Smax = 1.5 x 3 = 4.5 m So the suggested layout is satisfactory provided that the distance between lamps is not greater than 4.5m.

40m I I I I I I I I I I I I I I I I 12m

I I I So, 40m with 16spacings = 2.5m each space This is well below the Smax of 4.5 m 12m with 9 spacings = 1.33m each space I I I HALF SPACE HALF SPACE 1 SPACE 1 SPACE This is well below the Smax of 4.5 m 1 SPACE Therefore this layout should work. 1 SPACE

EXAMPLE A workshop is 12m by 6m by 4m high and has workbenches 1m high. Discharge lamps, each with an output of 3700lm, are to be fitted in aluminium industrial reflectors at ceiling level. The surfaces have reflectances of 0.7 for the ceiling and 0.5 for the walls. The light loss factor is 0.7. The illuminance required is 400 lux. Find the utilisation factor for the room Calculate the number of lamps required

EXAMPLE A classroom with an area 10m by 6m is illuminated by 18 tubular fluorescent lamps, where each lamp is 60W with a luminous efficacy of 80lm/W. The utilisation factor is 0.46 and the light loss factor used is 0.8. Calculate the average illuminance in the classroom.

EXAMPLE A lecture room which is 15m long, 10m wide and 4m high is to be illuminated by ceiling mounted luminaires each housing three compact 20 watt fluorescent lamps. Calculate the number and spacing of luminaires required if a minimum illuminance of 300 lux is required on the working plane (desk surface) which is 0.8m above the floor. Ceiling reflectance 0.7, wall reflectance 0.1 Lamp efficiency = 40 l/w LLF = 0.8 Max spacing to height ratio = 1.5