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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.
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Solution
Given,
Relative luminosity = 0.6
Let P be the radiant flux of the source.
∴ Luminous flux = P × 685
Again, relative luminosity
`="Luminous flux of a source of given wavelength"/"Luminous flux of a source of 555nm of same power"`
`therefore0.6="Luminous flux of a source P watt"/(685P)`
`rArr685 xxPxx0.6=120xx685`
`rArr P=120/0.6=200W`
So, 200 W radiant flux is needed to produce the same brightness sensation for 600 nm wavelength.
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