Total Radiation Law

The rate of loss of heat by radiation per unit area of the surface of a perfectly black body is directly proportional to the fourth power of its absolute temperature.

It must be clearly understood, however, that this 4th power law is not a law of cooling but a law of emission. It does not, therefore, refer to the net loss or transfer of heat by radiation due to exchange with its surroundings but only to total emission of radiation by the body by virtue of its temperature, irrespective of what it does or does not receive from the surroundings. Then, again, because it concerns itself with black bodies, it is also a law of radiation.