An infrared led is a led (light emitting diode) that emits light in the infrared part of the spectrum.

Infrared is a part of the non-visible light spectrum that is very useful to transmit remote control signals, measure obstructions between a source and a receiver, or measure distance.

Since an infrared led is a diode, it conducts like any diode, current in only one direction. That means polarity is important! An infrared led only emits light when used in the forward direction. If you look at the led from the top or bottom, the terminal at the flattened side of the housing is the cathode (negative) one.

Although humans cannot see infrared light, testing an infrared led is easy: take out your mobile phone and turn on the camera. Aim for the led and power it up. If you see a white/purple spot on your camera, the led emits light. This trick works with most camera’s, but not with all as some have built-in infrared filters.

Most important specifications

  • Forward voltage drop typical around 1.2 V
  • Maximum forward current (typical up to 100 mA).
  • Wavelength of emitted light (e.g. around 850 nm; nano meter, 1 nm = 1*10-9 m).
  • IR light ranges from 700 nm to 1000 nm. If you combine an IR LED with a IR Photo-transistor, be sure they match in terms of wavelength.