  We present results about photons production in relativistic heavy ion
collisions. The main novelty of our study is the calculation of the
contribution of the early stage photons to the photon spectrum. The initial
stage is modeled by an ensemble of classical gluon fields which decay to a
quark-gluon plasma via the Schwinger mechanism, and the evolution of the system
is studied by coupling classical field equations to relativistic kinetic
theory; photons production is then computed by including the pertinent
collision processes into the collision integral. We find that the contribution
of the early stage photons to the direct photon spectrum is substantial for
$p_T \approx 2$ GeV and higher, the exact value depending on the collision
energy; therefore we identify this part of the photon spectrum as the sign of
the early stage. Moreover, the amount of photons produced during the early
stage is not negligible with respect to those produced by a thermalized
quark-gluon plasma: we support the idea that there is no dark age in
relativistic heavy ion collisions.
