  There have been extensive experimental search for possible exciton superfluid
in semiconductor electron-hole bilayer systems below liquid Helium temperature.
However, exciton superfluid are meta-stable and will eventually decay through
emitting photons. Here we show that the light emitted from the excitonic
superfluid has unique and unusual features not shared by any other atomic or
condensed matter systems. We evaluate angle resolved photon spectrum, momentum
distribution curve, energy distribution curve and quasiparticle excitation
spectrum in the exciton superfluid and comment on relevant experimental data in
both exciton and exciton-polariton systems.
