Optics Question 511

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

Options:

A) 50W

B) 72W

C) $ 120\times {{(0.6)}^{2}}W $

D) 200W

Show Answer

Answer:

Correct Answer: D

Solution:

If h is the luminous efficiency of the bulb then.

luminous flux by 120 watt at 555 nm $ =\eta \times 120 $

Let bulb of P watt at 600 nm produces the same luminous flux as by 120 watt at 555 nm

then $ \eta \times 120=\eta P\times 0.6 $

$ \Rightarrow P=\frac{120}{0.6}=200\ watt. $



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