  High energy photon emission rate from matter created in Pb + Pb collisions at
CERN SPS energies is evaluated. The evolution of matter from the initial state
up to freeze-out has been treated within the framework of (3+1) dimensional
hydrodynamic expansion. We observe that the photon spectra measured by the WA98
experiment are well reproduced with hard QCD photons and photons from a thermal
source with initial temperature ~ 200 MeV. The effects of the spectral changes
of hadrons with temperature on the photon emission rate and on the equation of
state are studied. Photon yield for Au + Au collisions at RHIC energies is also
estimated.
