Question

The maximum illumination on a screen at a distance of 2 m from a lamp is 25 lux. The value of total luminous flux emitted by the lamp is

• A. 1256 lumen
• B. 1600 lumen
• C. 100 candela
• D. 400 lumen

Answer 1

Answer: (A)

1256 lumen

Answer 2

$I = \frac{L}{r^{2}} \Rightarrow L = I.r^{2} = 22 \times 2^{2} = 100$

Now $\varphi = 4\pi L = 4 \times 3.14 \times 100$= 1256 lumen.