Photon Statistics and Classical Fields

In view of the misunderstanding which surrounds the use of semiclassical methods in the treatment of optical coherence problems, a simple analysis is given which illustrates the generality of these methods. In particular, it is pointed out that, under commonly occurring circumstances, these methods apply at arbitrarily low light levels, and give correct results for the photoelectric counting of photons. The conclusions are illustrated by treating the interference between laser light and thermal light to demonstrate that this nontrivial case, recently treated by quantum field theory, is correctly described by semiclassical methods.