  We discuss the general features of the electromagnetic radiation from a
thermal hadronic gas as constrained by chiral symmetry. The medium effects on
the electromagnetic spectral functions and the partial restoration of chiral
symmetry are quantified in terms of the pion densities. The results are
compared with the electromagnetic radiation from a strongly interacting
quark-gluon plasma in terms of the leading gluon condensate operators. We use
the spectral functions as constrained by the emission rates to estimate the
electric conductivity, the light flavor susceptibility and diffusion constant
across the transition from the correlated hadronic gas to a strongly
interacting quark-gluon plasma.
