The Planck energy is the average energy of an oscillator,

(1)

The Planck postulate states that

(2)

where n is a nonnegative integer, h is Planck's constant, and is the frequency of radiation. Maxwell-Boltzmann statistics give

(3)

where C is a constant, k is Boltzmann's constant, and T is the temperature. Plugging in,

(4)

Planck Intensity Density, Planck Law, Simple Harmonic Oscillator--Quantum Mechanical