"Photoconductive materials (usually semiconductors) are those which become more electrically conductive when they absorb electromagnetic radiation from visible or ultraviolet light, infrared light or gamma radiation. The energy absorbed allows electrons to move from the valence band into the conduction band, increasing conductivity while the material continues to absorb the energy. Once the energy source is removed, the material loses conductivity again. Specific devices include photoresistors, photodetectors, charge coupled devices, photodiodes and phototransistors. Applications include photocopying (xerography), infrared and radiation detectors, street lights, clock radios and camera light meters"-- Provided by publisher.