  A conserved photon current is derived from the commutation relations
satisfied by the electromagnetic four-potential and field tensor operators. The
density is found to be a sum over positive and negative frequency terms, both
of which contribute a positive number density and propagate in a common
direction. Discrete positive and negative frequency excitations are both
identified as photons. Photon number, equal to the spatial integral of photon
density, is conserved in the absence of sources and sinks.
