Photoelectric cell; the light-sensitive component within a photosensor. The actual device might be a photodiode, a phototransistor, or a photoconductive cell. It is important to make a distinction between a photocell and a complete photosensor device. A photocell might be any device in which light controls the electron emission from a cathode, the electrical resistance of an element, or the electromotive force produced by a cell; it is usually incorporated in an electric circuit and used in mechanical devices such as door openers or home outdoor night lights.