On macroscopic description of photorefractive phenomena

A phenomenological approach, in which the current density is related in som e functional manner to the electric field and to the light intensity, is de veloped. The validity and advantages of this macroscopic formulation are di scussed by comparing its predictions with those derived from the particular microscopic models, Finally, some general phe nomenological equations are presented which include, among others, photon drag and the magneto-photovol taic effect.