For a thermal black body, the total amount of radiated energy E* in Watts per square

meter is proportional to the fourth power of the temperature of the body according the

relation E* = εσT^4. This formula had been deduced already in 1884 and

is called the Stefan-Boltzmann law. In this formula, T is the temperature of the body in

Kelvin and σ is the so-called Stefan-Boltzmann constant being 5,67 x 10^-8

W/m^2.K^4. The radiation factor ε has no dimension and it indicates to which

degree a certain body is a perfect thermally black body. The radiation factor therefore

is always smaller than one and for a non-perfect black body the curve of the

emission spectrum is proportionally lower while the relative distribution of the

wavelengths of the radiation roughly stays the same.