Question

Using the Lumen Method to find out how many fittings are required for a square conference room which requires 500 lux from CIBSE Guide, of area 200 m2, using the T5 fluorescent fittings at 1.2 meter long each and at 2 m high measured from the light source to the working surface.
The 1.2m T5 luminaire has 2700 lumens each.
Your answer should mention about all the light losses, say, due to surface reflectance at ceiling, wall and floor, light loss factor, maintenance factor, etc,.

Answer 1

Steps to be followed in Lumen Method

1. Assign required lux level

2. Select luminaire

3. Determine room index

4. Determine number of fixtures

N- Number of lamps required

E- Illuminaire level

A- Area at working p;ane

F- Average luminux flux from each lamp

UF – Utilisation factor

MF-Maintenance factor

Given

E= 500 lux

A= 200m2

F= 2700 lumens

To find utilization factor room index to be found out

Room index

Since is is square room

L=W= 14.14 m

H=2m given

From the Surface illuminated table For Reflectance 70% in ceiling,30% in Wall and 20% in floor

The value of UF =0.64

Assuming the Maintenance factor as 0.8

Number of luminaire

N= 72