  A semiclassical kinetic theory is presented for the fluctuating photon flux
emitted by a disordered medium in thermal equilibrium. The kinetic equation is
the optical analog of the Boltzmann-Langevin equation for electrons. Vacuum
fluctuations of the electromagnetic field provide a new source of fluctuations
in the photon flux, over and above the fluctuations due to scattering. The
kinetic theory in the diffusion approximation is applied to the
super-Poissonian noise due to photon bunching and to the excess noise due to
beating of incident radiation with the vacuum fluctuations.
