  The production of single photons in $Pb+Pb$ collisions at the CERN SPS as
measured by the WA98 experiment is analysed. A quark gluon plasma is assumed to
be formed initially, which expands, cools, hadronizes, and undergoes
freeze-out. A rich hadronic equation of state is used and the transverse
expansion of the interacting system is taken into account. The recent estimates
of photon production in quark-matter (at two loop level) along with the
dominant reactions in the hadronic matter leading to photons are used. About
half of the radiated photons are seen to have a thermal origin. The same
treatment and the initial conditions provide a very good description to
hadronic spectra measured by several groups and the intermediate mass dileptons
measured by the NA50 experiment, lending a strong support to the conclusion
that quark gluon plasma has been formed in these collisions.
