  The photon-number distribution between two parts of a given volume is found
for an arbitrary photon statistics. This problem is related to the interaction
of a light beam with a macroscopic device, for example a diaphragm, that
separates the photon flux into two parts with known probabilities. To solve
this problem, a Generalized Binomial Distribution (GBD) is derived that is
applicable to an arbitrary photon statistics satisfying probability convolution
equations. It is shown that if photons obey Poisson statistics then the GBD is
reduced to the ordinary binomial distribution, whereas in the case of
Bose-Einstein statistics the GBD is reduced to the Polya distribution. In this
case, the photon spatial distribution depends on the phase-space volume
occupied by the photons. This result involves a photon bunching effect, or
collective behavior of photons that sharply differs from the behavior of
classical particles. It is shown that the photon bunching effect looks similar
to the quantum interference effect.
