Counting Statistics of Photons Produced by Electronic Shot Noise

A theory is presented for the photodetection statistics of radiation produced by current fluctuations in a phase-coherent conductor. Deviations are found from the Poisson statistics that would result from a classical current. For detection in a narrow frequency interval $\delta \omega$, the photocount distribution has the negative-binomial form of blackbody radiation if $e\delta \omega$ is less than the mean current $\overline{I}$ in the conductor. When electronic localization sets in, $\overline{I}$ drops below $e\delta \omega$ and a different type of super-Poissonian photon statistics results.