Question

If luminous efficiency of a lamp is 2 lumen/watt and its luminous intensity is 42 candela, then power of the lamp is

• A. 62 W
• B. 76 W
• C. 138 W
• D. 264 W

Answer 1

Answer: (D)

264 W

Answer 2

Luminous flux$= 4\pi\mspace{6mu} L$ $= 4 \times 3.14 \times 42\mspace{6mu} = \mspace{6mu} 528$Lumen

Power of lamp $= \frac{\text{Luminous}\mspace{6mu}\text{flux}}{\text{Luminousefficiency}}$ $= \frac{528}{2}\mspace{6mu}\mspace{6mu} = 264\mspace{6mu} W$