Question

A source emits $31.4$ $W$ of radiant flux distributed uniformly in all directions. The luminous efficiency is $60lumen/W$. Find the luminous intensity of the source.

• A. $600$ $\pi$$Cd$
• B. $600$ $Cd$
• C. $150$ $Cd$
• D. $100$ $Cd$

Answer 1

Answer: (C)

$150$ $Cd$

The Radiant flux from source = $31.4W$

Solid angle = $4\pi$ (uniformly in all directions)
Luminous efficiency = $60lumen/W$
So, Luminous intensity is given as:

$=\frac{Luminousflux}{4\pi }=\frac{60\times 31.4}{4\pi }$

$\Rightarrow 150Cd$