Question

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

Answer 1

Given,
The luminous flux of the given source is 450 lumen/watt.
$\mathrm{We}\mathrm{know}that\mathrm{luminous}\mathrm{flux}\mathrm{of}555\mathrm{nm}\mathrm{source}\mathrm{of}1W=685\mathrm{lum}ens$
∴ Relative luminosity is given by,

$\frac{\mathrm{Luminous}\mathrm{flux}\mathrm{of}\mathrm{the}\mathrm{source}\mathrm{of}\mathrm{given}\mathrm{wavelength}}{\mathrm{Luminous}\mathrm{flux}\mathrm{of}555\mathrm{nm}\mathrm{source}\mathrm{of}\mathrm{same}\mathrm{power}}=\frac{450}{685}=66\%$

So, the relative luminosity at the wavelength emitted is 66 %.