Stefan–Boltzmann Law of Thermal Radiation

The law states that the rate of radiation heat transfer per unit area from a black surface is directly proportional to fourth power of the absolute temperature of the surface and is given by,

where T_s is absolute temperature in K; and σ is proportionality constant and called as Stefan–Boltzman constant equal to 5.67 × 10^{− 8} W/m²K⁴. The heat flux emitted by a real surface is less than that of black surface and is given by,

where ε is radiative properties of surface, called emmissivity.

The net rate of radiation heat exchange between a real surface and its surrounding is

where T_∞ and T_s are surrounding and surface temperature in K, respectively.