## Photon statistics

Photon statistics are the case of

Bose-Einstein statistics
with an unspecified total number of particles. The average
number of particles in a state

*s* is given by the

Planck distribution:

<*n*_{s}> = 1/(exp(*E*_{s}/
*k*_{B}T) - 1)

where *E*_{s} is the energy of a particle in *s*,
*T* is the temperature,
and *k*_{B} is Boltzmann's constant.

Black body radiation may be described through photon statistics:
the continuous absorption and re-emission of photons by the
walls of the body, which has nonzero volume and temperature.