LED: Light Emitting Diode

An LED, which stands for light-emitting diode, is a semiconductor diode that glows when a voltage is applied. These devices are used everywhere in your electronics, new types of lighting, and digital television monitors.

How an LED Works

Compare how the light-emitting diode works to the older incandescent lightbulb. The incandescent light bulb works by running electricity through a filament that is inside the glass bulb. The filament heats up and glows, and that creates the light; however, it also creates a lot of heat. The incandescent light bulb loses about 98% of its energy-producing heat making it quite inefficient.

LEDs are part of a new family of lighting technologies called solid-state lighting; LEDs are cool to the touch. Instead of one lightbulb, in an LED lamp there are many small light-emitting diodes.

LEDs are based on the effect of electroluminescence, where certain materials emit light when electricity is applied. LEDs have no filament that heats up but are illuminated by the movement of electrons in a semiconductor material, usually aluminum-gallium-arsenide. The light emits from the pn junction of the diode. How an LED works is complex but understandable if you examine the details.

Background

Electroluminescence, the natural phenomena upon which LED technology is built, was discovered in 1907 by British radio researcher and assistant to Guglielmo Marconi, Henry Joseph Round, while experimenting with silicon carbide and a cat's whisker.

During the 1920s, Russian radio researcher Oleg Vladimirovich Lossev was studying the phenomena of electroluminescence in the diodes used in radio sets. In 1927, he published a paper called "Luminous Carborundum [silicon carbide] Detector and Detection With Crystals" detailing his research, and while no practical LED was created at that time based on his work, his research did influence future inventors.

Years later in 1961, Robert Biard and Gary Pittman invented and patented an infrared LED for Texas Instruments. This was the first LED; however, since it was infrared, it was beyond the visible light spectrum. Humans cannot see infrared light. Ironically, Baird and Pittman only accidentally invented a light-emitting diode while they were actually attempting to invent a laser diode.

Visible LEDs

In 1962, Nick Holonyack, a consulting engineer for General Electric, invented the first visible light LED. It was a red LED and Holonyack had used gallium arsenide phosphide as a substrate for the diode. Holonyack has earned the honor of being called the "Father of the light-emitting diode" for his contributions. He also holds 41 patents and his other inventions include the laser diode and the first light dimmer.

In 1972, electrical engineer, M George Craford invented the first yellow-colored LED for Monsanto using gallium arsenide phosphide in the diode. Craford also invented a red LED that was 10 times brighter than Holonyack's.

Monsanto was the first company to mass-produce visible LEDs. In 1968, Monsanto produced red LEDs used as indicators. But it was not until the 1970s that LEDs became popular when Fairchild Optoelectronics began producing low-cost LED devices (less than five cents each) for manufacturers.

In 1976, Thomas P. Pearsall invented a high-efficiency and extremely bright LED for use in fiber optics and fiber telecommunications. Pearsall invented new semiconductor materials optimized for optical fiber transmission wavelengths. In 1994, Shuji Nakamura invented the first blue LED using gallium nitride.

More recently, as of May 2020, Arrow Electronics, a Fortune 500 firm that provides services related to electronic components and computer products, noted the most recent development in LEDs:

"...scientists have developed a technique that allows for a single LED to produce all three primary colors. This has big implications for active LED displays, which normally require three to four tiny, individual LEDs placed near each other to render the full spectrum."

Sources

• “Current State of LEDs: Latest LED Technology.” Arrow.com, 31 May 2020
• Lossev, O. V.. "Luminous Carborundum Detector and Detection With Crystals." The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 6(39), 1024–1044, 1 Nov. 1928. doi:10.1080/14786441108564683.