Hello Prabhukrupa,

There's no single answer as it depends on what you're trying to measure.

The power in a light beam? (a bolometer)

The spectral makeup of a light ray? (a spectrometer)

etc.

If you're trying to measure one photon (who knows...) then knowing the wavelength of interest is crucial - the apparatus to detect a visible photon is different from that needed to pick up a hard x-ray photon.