Abstract
The joint probability of detecting simultaneously three photons at three different points in the superposition field of two independent plane waves with random phases is calculated and compared with the results of a classical wave theory. There are important differences when the number of photons is small. In particular, if there is one photon in one beam and two photons in the other one, three photodetectors can be placed at positions such that all three never respond at once, even though one beam intensity is two times stronger than the other.