F F1157 Pages: 3

b) Explain inverse square law and Lamberts cosine law with the help of neat (4)
sketches

c) Four lamps 15m apart are arranged to illuminate a corridor. Each lamp is (4)
mounted at a height of 8൩ above the floor level. Each lamp gives 450 Cd in all
directions below the horizontal. Find the illumination at the point ‘P’
midway between second and third lamp.

{4 (2 ‏ها ها‎
இருகி ட்‌ ١ ‏يه‎ 8
1 0 \ ‏و0‎ 08. 0 5
82, 03
8m ட்‌ 8m
> ‏“و‎ :

ടി]
7.5m

(15 m—>}=—15 ‏م ممع‎ 15 m—|

PART C
Answer any two full questions, each carries10 marks.
12 ൮ An office 30m x 15m is illuminated by twin 40W fluorescent luminaries of (4)
lumen output 5600 lumens. The lamps being mounted at a height of 3m from the
work place, the average illumination required is 240 lux. Calculate the number of
lamps required to be filled in the office, assuming the coefficient of utilization to
be 0.6 and maintenance factor to be 0.8. Space to mounting height ratio is 1.25.
b) What is ULOR and DLOR? How these parameters aid in selecting luminaries for (4)
different applications.
c) Calculate the room index for a hall of dimensions 10m X 8m X 3m. Luminaries (2)
are suspended at height of 0.8m from the ceiling and work plane height is 0.85
from floor.
13 ஐ Define (2)
1. Coefficient of utilisation

2. Depreciation factor

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