The luminous flux of a monochromatic source of 1 W is 450 lumen `W^-1`. Find the relative luminosity at the wavelength emitted.

Explanation

The luinous flux of the given source of 2W is 4500 lumen/watt
`:. Relative luminousity
Luminous flux of the source
`=(of given wavelength)/(Luminous flux of 555 nm)`
source of same power
`=450/685=66%`
`[:.` since luminous flux of 555 nm source of 1W=685 lumen]`