Infrared LED

A infrared LED (short IR-LED or IRED ) is a specific light-emitting diode ( English light emitting diode , LED, therefore infrared diode ) light in the near infrared region with a wavelength of 700 nm to 1000 nm emitted. This area of ​​the light spectrum is not visible to the human eye , but can be measured with radiation detectors made of pyroelectric materials or semiconductors , for example with photodiodes or phototransistors . Unless an infrared filter is installed, digital cameras are sensitive to both visible and infrared light. With their help, for example, the functionality of infrared remote controls can easily be checked.

Photo of an 8 mm, 5 mm and a 3 mm LED (from left to right).
A matchstick as a yardstick

Infrared LEDs were the first light emitting diodes manufactured and were developed before the first red light emitting diodes. In 1961 Robert Biard and Gary Pittman patented the first gallium arsenide (GaAs) based infrared LED at Texas Instruments . Up until the early 1970s, the only light-emitting diodes available - red and infrared LEDs - were very expensive at unit prices of around US $ 200 and therefore had little practical significance. As a comparison, the wholesale price of IR LEDs in larger numbers in 2010 was less than 20 cents.

Infrared LEDs are manufactured with a wavelength of 840 nm, 850 nm, 875 nm, 880 nm, 885 nm, 890 nm, 940 nm and 950 nm. The 940 nm version based on aluminum gallium arsenide has lower manufacturing costs and is widely used because of its use in IR remote controls. The semiconductor gallium arsenide, which is also used for infrared LEDs, has a direct band gap of 1.4  eV , corresponding to a wavelength of 885 nm.

application

Infrared LEDs are used in simple data transmission systems such as infrared remote controls ( television , radio , etc.) or the IrDA infrared interface in cell phones and mobile computers .

Another area of ​​application is alarm and security technology, for example in light barriers or motion detectors . In this area, they also serve as a source of illumination for surveillance cameras or certain night vision devices .

Individual evidence

1. ^ The first LEDs were infrared ( Memento from April 1, 2010 in the Internet Archive ), in The Quartz Watch , The Lemelson Center , accessed on March 9, 2010