Stefan-Boltzmann law states that the total emissive power of a blackbody, Eb, is given by:
Eb = σ T4
where σ is the stefan-Boltzmann constant and T is the absolute temperature of the blackbody. The value of the Stefan-Boltzmann constant is 5.67x10-8 W/m2 K4 or 3.3063 x 10-15 Btu/s.in2.F4. The spectral variation of blackbody radiation is described by the Planck distribution . Integrating the Planck distribution law over all wavelengths (λ) gives the Stefan-Boltzmann law.
When a blackbody of a surface area (A) is immersed in a medium with ambient temperature Ta, the net rate of heat radiated by the blackbody is given by:
Qradiation = σ A ( Ts4 - Ta4 ), Ts> Ta .
where:
Ts = Absolute temperature of the blackbody
Ta = Absolute temperature of the surrounding medium (ambient temperature)