According to Stefan's law, the total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature. Stefan Boltzmann law is applicable for heat transfer by radiation.

The term radiation is applied to the kinds of processes which transmit energy by means of electromagnetic waves. The amount of radiation mainly depends upon the nature of body, temperature of the body and type of surface of the body.

when the radiations are falling on a body, three things happen, i.e. a part of the radiations are absorbed by the body, a part of the radiations are reflected and the remaining radiations are transmitted through the body.