Know Thy LED


The invention of the LED is one of the most important discoveries of our times. They are everywhere, from our flashlights to household lighting and television sets. We don’t need to tell you that a project with more blinkies is better than a project with fewer blinkies. But an LED is not simply an LED; the sheer variety of LEDs is amazing, and so in this write-up, we’ll take a closer look at how to choose the right LED for your next masterpiece.

The LED Family Tree

The first official LED was created in 1927 by Russian inventor Oleg Losev, however, the discovery of electroluminescence was made two decades prior. British experimenter H. J. Round of Marconi Labs was the first to report the phenomenon in 1907. He found that silicon carbide would glow with a yellowish light when a potential of ten volts was applied to it. This set off years of experimenting with materials such as silicon carbide, gallium arsenide, gallium antimonide, indium phosphide, and silicon-germanium in an attempt to create a practical device.

In 1955, Rubin Braunstein reported infrared emission from gallium arsenide, however James R. Biard and Gary Pittman of Texas Instruments presented the first IR lamp (PDF) in 1961 which was the first practical LED to be patented in the August of the same year. Consequently, the first commercial LED was an IR LED with 890 nm light output and was called the SNX-100.

The era of the visible LED began in 1962 by Nick Holonyak, Jr. who was working at General Electric at the time. He discovered the red LED and published the results in the Applied Physics Letters on December 1, 1962 and currently holds around 41 patents to his name. He is known as the father of the visible LED and is also responsible for the laser diode commonly used in CD and DVD players. A decade later came the discovery of the yellow LED, M. George Craford, who happens to be a former graduate student of Holonyak.

 

The LED that Won the Nobel Prize

In 2014, three scientists, Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura won the Nobel prize for inventing the blue LED in the early 1990s. Although RGB LEDs are obviously not possible without the “B”, the invention of the blue LED was important beyond the color. Blue LEDs are bright and efficient, and were the last stepping stone towards producing the white LED that illuminates the world today.

There are two methods to create white light from LEDs. The obvious method involves mixing three primary colors in the correct proportions to produce white illumination. The second method which is used to make white LEDs is the phosphor method where the blue LED shines onto a yellow phosphor coating.

In this method, the blue LED is used in conjunction with a yellow phosphor coating. The idea is to have part of the blue light converted into yellow light and leave a part of it in its original wavelength. When both these lights combine, they form a white beam which is far more efficient and pure than that from the first method.

Believe it or not, this discovery of color combination was made by Sir Isaac Newton in the early 1700s.

Behind their Glowing Personality

Regardless of the color, LEDs are all electroluminescent. Electroluminescence is the phenomenon wherein a material emanates light when an electrical current is passed through it. The underlying process involves the recombination of electrons and holes in the material. Check out this video for a quick summary and visualization.