# Planck's Law

The
spectral radiance
(**B _{v}**) 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

**k**the Boltzmann constant. Note that in this formulation, spectral radiance is equal to the energy (

_{B}**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.