Out of the following what is used to detect the intensity of light ?

A photodiode is a p-n junction diode fabricated with a transparent window to allow light to fall on the diode.

It is operated under reverse bias. When the photodiode is illuminated with light (photons) with energy greater than the energy gap of the semiconductor, electron-hole pairs are generated due to the absorption of photons.

Due to the electric field of the junction, electrons and holes are separated before they recombine. The magnitude of the photocurrent is directly proportional to the intensity of incident light.

Thus, a photodiode in reverse bias is used to detect the intensity of light.

Answer: Photodiode in reverse bias