10 LED Projects for Geeks by John Baichtal

Author:John Baichtal
Language: eng
Format: epub
Publisher: No Starch Press
Published: 2018-07-05T16:00:00+00:00

FIGURE 6-1: The electromagnetic spectrum

Infrared LEDs

Infrared LEDs have been around since the early 1960s. In fact, they were invented a year or two before LEDs that emit visible light. Figure 6-2 shows an example of an infrared LED.

FIGURE 6-2: An infrared LED. The larger section visible inside corresponds to the negative lead.

Like all diodes, an LED is a semiconductor. Current passes through a diode more easily in the forward direction than it would in reverse. It also emits a small quantity of electromagnetic radiation as it moves forward through the diode. Where this emission lies on the electromagnetic spectrum depends upon what materials were used to manufacture the diode. Regular diodes made of silicon and germanium do not tend to emit light, while other semiconductor materials can emit various colors of visible light, as well as ultraviolet and infrared. Infrared LEDs are usually made with gallium arsenide (GaAs) or aluminum gallium arsenide (AlGaAs).

When an LED is reverse-biased (hooked up backward), no light will be produced.

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