The photorefraction in LiNbO3 and LiTaO3 crystals is studied depending on exposure time, light intensity (0.1-105 W/cm2), temperature (115-500 K) as well as photorefraction based effects of the anisotropic amplification of scattered light and self-enhancement of holograms. The conclusions are made about the anomalous influence of laser irradiation on the crystal conductivity and at least two kinds of photorefractive centres (F, F+ and Fe2+, Fe3+ centres). The model of complementary holographic gratings is proposed which explains the main properties of the self-enhancement effect, and enables us to estimate the free mean path of the electrons which take part in the bulk photovoltaic effect (≈80 nm), the photoexcitation quantum efficiency (≈10-4) and the product of the electron mobility and their lifetime in the conduction band (≈10-9cm2/V) for LiNbO3: Fe.