The ZOS-T1810-A05 consist of an infrared emitting diode and an NPN silicon phototransistor, encased side-by-side on converging optical axis in a black thermoplastic housing.The phototransistor receives radiation from the IR
only .This is the normal situation. But when an object is in between , phototransistor could not receives the radiation.For additional component information , please refer to IR and PT.