  In connection with recent studies of extremely long-living spin-cyclotron
excitations (actually magneto-excitons) in a quantum Hall electron gas, we
discuss contribution to the light-absorption related to the presence of a
magneto-exciton ensemble in this purely electronic system. Since the weakly
interacting excitations have to obey the Bose-Einstein statistics, one can
expect appearance of a coherent state in the ensemble. A comparative analysis
of both incoherent and coherent cases is done. Conditions for a phase
transition from the incoherent state to the coherent one are discussed.
