IR INTRUDER CKT: Infrared LED & Phototransistor Pair 5mm Pair of Infrared LED and Photo diode tuned to IR wavelength IR Transmitter & Receiver PairUse this 5 mm ir transmitter and receiver pair to build object sensors, color sensors, linesensors, distance sensors, etc. Both the transmitter and receiver are built to work on the940 nm wavelength. Note: the transparent led is transmitter while the dark blue one is the receiver.transistor