  We compute the thermal photon spectrum in the Pb+Pb collisions at the CERN
SPS energy using thermal emission rates and a hydrodynamic description for the
evolution of produced hot matter and compare our results with the measurements
of the excess photons by the WA98 collaboration. Our results show that the
measured photon spectrum can be reproduced with realistic initial conditions
which take properly into account also the finite longitudinal size of the
initial collision zone and which simultaneously describe well both the
transverse and longitudinal hadron spectra. In the scenario with initial
formation of QGP the recently calculated emission rate, complete to order
alpha_s, reproduces the measured spectrum. However, the experimental spectrum
can also be reproduced in a purely hadronic scenario without transition to QGP
state, but a high initial temperature, much over the values predicted for the
phase transition temperature T_c, is required.
