Use this 3 mm IR Transmitter and Receiver pair to build object sensors, colour sensors, line sensors, distance sensors, etc.
Both the transmitter and emitter are built to work on the the 940 nm wavelenght.
Use these 3 mm IR Transmitter and Receiver in places where a 5 mm IR Transmitter and Receiver cannot is too big to fit in. These sensors are perfect for making custom wheel encoders.
Note: The transparent LED is transmitter while the dark blue one is the receiver.