Planck’s Law
The spectral radiance (Bv) from a black body whose surface is at temperature (T) in Kelvin. h is the Planck constant, ν (the Greek letter Nu) the frequency of the radiance, c the velocity of light, and kB the Boltzmann constant. Note that in this formulation, spectral radiance is equal to the energy (hν) according to the Planck postulate times two terms that represent the amount at each frequency.
At very low frequencies, Planck’s Law tends to the Rayleigh-Jeans law, while at very high frequencies it tends to the Wien approximation. Plot below from Wikipedia.
