The mathematical description of photorefraction in crystals has been established over two decades.

Although not every detail of this model has been verified yet, for the case of amorphous organic photorefractive materials, this standard model has naturally formed the basis of their development. The model is outlined here for the important case of an hole transport matrix with a single kind of trapping level. In the case of crystals it has been possible to refine this model as necessary to account for idiosyncrasies of the behavior of specific materials.