Stefan-Boltzmann law (Stefan, L. Boltzmann): The radiated power P (that is the rate of emission of electromagnetic energy) of a hot body is proportional to the radiating surface area, A, and the 4th power of the thermodynamic temperature, T. The constant of proportionality is Stefan-Boltzmann constant. Scientifically,
P = e sigma A T4,
Here the efficiency rating e is termed as the emissivity of the object.