The energy radiated by a blackbody radiator per second per unit area is proportional to the fourth power of the absolute temperature and is given by
For hot objects other than ideal radiators, the law is expressed in the form:
where e is the emissivity of the object (e = 1 for ideal radiator). If the hot object is radiating energy to its cooler surroundings at temperature Tc, the net radiation loss rate takes the form
The Stefan-Boltzmann relationship is also related to the energy density in the radiation in a given volume of space.