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Question
A source emits 31.4 W of radiant flux distributed uniformly in all directions. The luminous efficiency is 60 lumen watt−1. What is the luminous intensity of the source?
Solution
Given that,
Radiant flux = 31.4 W
Since the radiant flux is distributed uniformly in all directions, the solid angle will be 4π Luminous efficiency = 60 lumen/W
So, luminous flux = luminous efficiency × radiant flux
= 60 × 31.4 lumen
Luminous intensity = `"Luminous flux"/"Solid angle"="Luminous flux"/(4pi)`
`=(60xx(31.4))/(4pi)`
= 150 candela
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