Question

A conference room of size 25 m \(\times\) 12 m is illuminated by CFL having efficacy of 60 lumen/W. The lighting power density (LPD) of the room is 12 \(\text{W/m}^2\). If the utilization and maintenance factors are 0.8 and 0.5, respectively, then the estimated illumination level (in lux) of the conference room is (in integer).

Hint:

Illumination (lux) = LPD \(\times\) lamp efficacy \(\times\) utilization factor \(\times\) maintenance factor; the room area cancels out since LPD is already stated per unit area.

Answer 1

Correct Answer: 288

Step 1: Understanding the Question:
We need to find the illumination level (in lux) produced inside a conference room, given the lighting power density (LPD), the lamp efficacy, and two factors, the utilization factor and the maintenance factor, that account for real-world light losses.

Step 2: Key Formula or Approach:
The lighting power density (LPD) tells us how many watts of lighting power are installed per square metre of floor area. Multiplying LPD by the lamp efficacy gives the raw lumens produced per square metre.
\[ \text{Installed lumens per } m^2 = \text{LPD} \times \text{Efficacy} \]
Not all of this light reaches the working plane. The utilization factor (UF) accounts for light lost to fittings, room surfaces, and room geometry, and the maintenance factor (MF) accounts for light lost due to dust, lamp aging, and dirt on fittings over time. The actual illumination level (lux, i.e. lumens per square metre reaching the work plane) is
\[ E = \text{LPD} \times \text{Efficacy} \times UF \times MF \]
Because LPD is already defined per unit area, the room's overall floor area (25 m \(\times\) 12 m = 300 \(m^2\)) cancels out of this ratio and is not needed directly.

Step 3: Detailed Explanation:
Given: LPD \(= 12\ \text{W/m}^2\), Efficacy \(= 60\) lumen/W, \(UF = 0.8\), \(MF = 0.5\).
First find the installed lumens per \(m^2\):
\[ 12 \times 60 = 720\ \text{lumen/m}^2 \]
Now apply the utilization factor:
\[ 720 \times 0.8 = 576\ \text{lumen/m}^2 \]
Now apply the maintenance factor:
\[ 576 \times 0.5 = 288\ \text{lumen/m}^2 = 288\ \text{lux} \]

Step 4: Final Answer:
The estimated illumination level of the conference room is 288 lux. \[ \boxed{288} \]