The Stefan-Boltzmann constant, symbolized by the lowercase Greek letter sigma ( ), is a physical constant involving black body radiation. A black body, also called an ideal radiator, is an object that radiates or absorbs energy with perfect efficiency at all electromagnetic wavelength s. The constant defines the power per unit area emitted by a black body as a function of its thermodynamic temperature .
According to a principle of physics called Stefan's law , the relationship between emitted power per unit area (in watt s per square meter, denoted M ) and thermodynamic temperature (in kelvin s, denoted T) is:
M = T 4
That is, the power per unit area is directly proportional to the fourth power of the thermodynamic temperature.
The value of the Stefan-Boltzmann constant is approximately 5.67 x 10 -8 watt per meter squared per kelvin to the fourth (W · m -2 · K -4 ).
Also see Table of Physical Constants .