Comparative study of photon bunching of classical fields

Previous work on the two-time photon-number correlations of quantum non-sta tionary fields has focused on the demonstration of self-contradictory predi ctions of the photon antibunching according to different definitions. In th is paper we analyse the usefulness of the conventional and generalized defi nitions of photon bunching in a description of classical non-stationary lig ht. It is proved that the generalized definition applied to classical field s predicts photon bunching but never antibunching. In contrast, the two con ventional definitions are shown to improperly classify certain classical no n-stationary fields as being antibunched.