IR transmitter led (940mm)

An infrared light-emitting diode (LED) is not used to light up screens and monitors the way other LEDs are; instead, it is often used for non-visual applications and for nighttime illumination. The application of an infrared LED depends on its nanometers (nm), or its wavelength, with the common usage being between 808nm and 940nm. Infrared LED devices are used in everyday life in TV remote controllers and automated card readers. The use of infrared LEDs can be separated into two types: direct and reflecting, and the manner in which the infrared LED and the receiving diode interact determines the LED's uses. 

Here is a great video using infrared LED's as n proximity sensor to allow the microcontroller to determine how far the object is playing piano notes accordingly. This is called n Theremin introduced in the 1920's.