In

Physics, an

expression for the

distribution of radiation in a black-body

radiator.

Evdv = 8pi h(v^3) / c^3(e^(hv/kT) - 1 )^dv

Where E = th energy density radiated at a temperature T within the narrow frequency range from v to v + d v. h is Planck's constant, c the velocity of light, e the base of the natural logarithms and k Boltzmann's constant.