A Phototransistor is a two-lead or three-lead semiconductor that is more sensitive than a photodiode. It senses light levels and uses them to alter currents to create an electrical signal. The bipolar semiconductor is can be made from silicon or another semi-conductive material. How do Phototransistors work? Once detection of light such as IR (infrared), visible light or UV (Ultraviolet) is successful, the device will alter a current flowing between an emitter and collector, depending on the light and level of intensity it receives. Features and Benefits Reflow surface-mounting support Small, ultra-thin High sensitivity Electromagnetic noise resistance High linearity Produce a higher current than photodiodes Where might I use a Phototransistor? A photo transistor can be used in many different devices and applications such as: Photo interrupters Industrial electronics Human detection devices TV Air conditioning Digital photo-frames PCs or Laptops Automatic switches (lighting equipment) IP cameras Security devices Home electronics