Stefan Boltzmann law is applicable to

The Stefan-Boltzmann law for the emissive power gives the total energy emitted by a blackbody.

E_b = σT⁴

where E_b is the emissive power of a blackbody, T is absolute temperature, and σ (= 5.67 X 10^-8 W/m²/K⁴) is the Stefan-Boltzmann constant.

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A black body is an object that absorbs all the radiant energy reaching its surface. No actual body is perfectly black; the concept of a black body is an idealization with which the radiation characteristics of real bodies can be compared.

Properties of the black body:

• It absorbs all the incident radiation falling on it and does not transmit or reflect regardless of wavelength and direction
• It emits the maximum amount of thermal radiation at all wavelengths at any specified temperature
• It is a diffuser emitter (i.e. the radiation emitted by a black body is independent of direction)