  We theoretically study cooperative effects in the steady-state transmission
of photons through a medium of $N$ radiators. Using methods from quantum
transport, we find a cross-over in scaling from $N$ to $N^2$ in the current and
even higher powers of $N$ in the higher cumulants of the photon counting
statistics as a function of the tunable source occupation. The effect should be
observable for atoms confined within a nano-cell with a pumped optical cavity
as photon source.
