Statistical physics of Bose-Einstein condensed light in a dye   microcavity
  We theoretically analyze the temperature behavior of paraxial light in thermal equilibrium with a dye-filled optical microcavity. At low temperatures the photon gas undergoes Bose-Einstein condensation (BEC), and the photon number in the cavity ground state becomes macroscopic with respect to the total photon number. Owing to a grandcanonical excitation exchange between the photon gas and the dye molecule reservoir, a regime with unusually large fluctuations of the condensate number is predicted for this system that is not observed in present atomic physics BEC experiments. 
Jan Klaers, Julian Schmitt, Tobias Damm, Frank Vewinger, Martin Weitz
cond-mat.quant-gas