What Are Light Emitting Diodes (LEDs) and How Do They Work?

Chances are, you see light emitting diodes (LEDs) every day. They are used to illuminate all kinds of public spaces, displays, technology screens (you might be reading this through one right now) and they are put to myriad uses in daily life. But have you ever wondered how they actually work to emit light? Here is an overview of the science behind LEDs.

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How Do LEDs Produce Light?

Unlike a standard (incandescent) bulb, an LED doesn't have a filament inside of it. Instead, it uses a semiconductor that is coated with a material to make it conduct electricity, which then produces light. Typical LED lights use silicon crystals, which are semiconductors that have a stable electron bond. The coating destabilizes that electron bond and allows the crystals to conduct electricity. Negative electrons then flow into what are called holes in P-type (positively charged) material, emitting light as they do so. The current of electricity flows between the anode and cathode of the LED light and its battery.

What Determines the Color of an LED?

The color of an LED is determined by the material used in the semiconductor chip, the wavelength of the light and the band gap (the state in the semiconductor where no electrons can exist). While many use silicon, other materials are more common in colored LED lights. The wavelength is highest for infrared LEDs and gets progressively lower as you look at colors moving down the rainbow spectrum from red to violet, with white and pink having a broader spectrum of wavelengths. Aluminium gallium arsenide (AlGaAs) is used for infrared and red LEDs. Gallium arsenide phosphide (GaAsP) is used in red, orange, and green LEDs. Aluminium gallium indium phosphide (AlGaInP) and Gallium(III) phosphide (GaP)  are used in red, orange, yellow, and green colors. Indium gallium nitride (InGaN) is used for pure green, blue, and violet.

This is just a brief overview of how LEDs work. They are more sustainable than standard lights and are found in a variety of brightnesses, from the kind seen on holiday decorations to ones that light up entire billboards.