Question

The relative luminosity of wavelength 600 nm is 0.6. Find the radiant flux of 600 nm needed to produce the same brightness sensation as produced by 120 W of radiant flux at 555 nm.

Answer 1

Relative luminousity =Luminous flux of a source of given wavelength / Luminous flux of a source of 555 nm of same power
Let the radiant flux needed be P watt.
Ao, 0.6 =Luminous flux of source 'P' watt / 685 P
Luminous flux of the source = (685 P)× 0.6 = 120 × 685
=>P =120 / 0.6
= 200W