Concepts Of Physics MCQ Edition [Volume 1]PhysicsPhotometry
A light source produces monochromatic light of wavelength 555 nm . It consumes 100 W of electric power and emits 35 W of radiant flux. Compute the overall luminous efficiency.
Options
- A240 lumen/W
- B685 lumen/W
- C120 lumen/W
- D350 lumen/W
Correct answer
A. 240 lumen/W
Step-by-step solution
The relative luminosity of light of wavelength 555 nm is 1 . The luminous flux corresponding to 1 W of radiant flux at 555 nm is 685 lumen . Total luminous flux emitted by the source is given by: _v = 35 W 685 lumen/W = 23975 lumen The overall luminous efficiency is defined as the ratio of the total luminous flux to the total electric power consumed by the source. Overall luminous efficiency = 23975 lumen 100 W = 239.75 lumen/W Rounding off to the nearest integer, we get 240 lumen/W .