Question

Define intensity of radiation on the basis of photon picture of light. Write its S.I. unit.

Answer 1

The amount of light energy/photon energy, incident per meter square per second is called intensity of radiation. 

SI Unit:  W/m² or Joule/Sec-meter² 

Answer 2

The amount of light energy / photon energy, incident per metre square per second is called intensity of radiation.

SI Unit : W/m² or Joule/Sec-meter²