Liquid crystal (LC) spatial light modulators (SLMs) are addressed optically with semiconductor thin-film photosensors incorporated into the devices. Nematic LCs, which are insensitive to the polarity of the applied voltage, are addressed by optically modifying the effective resistance of the photosensors to be much smaller than or much larger than a threshold value. Much faster ferroelectric LCs, which are polarity sensitive, are addressed by supplying sufficient photogenerated charge. Because the spatial resolution of the devices decreases rapidly with increasing mobility of carriers at the photosensor/LC interface, very low mobilities, less than 1 cm2 V-1 s-1, are required. Photodiodes of hydrogenated amorphous silicon in p-i-n, Schottky, and metal insulator semiconductor configurations form practical photosensors for optically addressed SLMs. Thin-film photoconductors, having nonblocking contacts, cannot be used in many cases because of their large dark currents.