The grating spacing dependence of photorefractive diffraction efficiency in an organic polymer composite is presented and discussed. The analysis of the grating spacing dependence of the refractive index modulation with the standard model of photorefractive grating dynamics is shown to lead to inconsistencies in determination of the maximum attainable index change. It is shown that the effects resulting from orienting of the composite’s optically second‐order nonlinear chromophores in the periodic local field affect the formation of the refractive index grating. ©1995 American Institute of Physics.