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In a display window of height H = 8.66 m, of a retail store, a luminary of intensity L is mounted at a distance L = 5 m away from the rear. Its light beam is cast at an angle of 45° from the ceiling, as shown in the figure alongside.
The ratio of illumination at points P1 and P2
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- 1 : √3
- √3 : 2
- √2 : 1
- 1 : √2
Correct Option: C
In a display window of height H = 8.66m of retail store, a luminaire of intensity I is mounted at a distance L = 5cm from the rear. Its light beam is cast at an angle of 45 degree from the ceiling as shown in the given figure. The ratio of illumination at Points P1 and P2 is √2 : 1 by using the Inverse square law.
The ratio of intensity at points P1 and P2 is the inverse ratio of distance of these points from the light source.
1/(5/cos45)² : 1/(5/cos60)² = (5/cos45)² : (5/cos60)²
= cos60² : cos45²
= 1/4 : 1/2 = 1 : 2
