The (Accidental) Invention of the LED

By Taryn Engmark

Assistant Editor

Embedded Computing Design

October 20, 2021

Story

The (Accidental) Invention of the LED

From the lamp in your living room to unpleasantly bright headlights, LEDs are everywhere these days. So much so that we take them for granted, and the long, almost completely accidental road it took for them to reach a light socket near you.

Today’s light-emitting diodes offer high levels of luminosity at the extremely low power consumption that we all enjoy. But LEDs have been in the making for over a century, taking baby steps to get to where they are now. 

In the Beginning, There Was L(ED)ight

Let’s start at the birth of the LED, way back in the early 1900s.

The 1900s-1920s: Electroluminescence

LEDs operate through a process known as electroluminescence – a phenomenon where semiconductor materials produce light when electrons move through them. This process was accidentally discovered in 1907 by Henry Joseph Round, a British engineer who was performing experiments with silicon carbide and a cat’s whisker (or crystal) detector.

The cat’s whisker detector, a form of crystal detector, was used by Henry Joseph Round when he accidentally discovered electroluminescence while experimenting with silicon carbide. (EEWeb)

Although Round discovered the process that led to the creation of the LED, research was furthered by Russian inventor Oleg Losev in the 1920s. He published his findings in journals across Europe, but none of his research was practically used for several decades. 

The 1960s: The First Practical LED

In 1961, Robert Biard and Gary Pittman stumbled upon the creation of a low-intensity near-infrared LED that they later patented for Texas Instruments. This LED featured light emission from a tunnel diode made on a gallium arsenide (GaAs) substrate (Figure 1). A year after their discovery, in 1962, TI released their first commercial LED product, the SNX-100, which used a GaAs crystal and emitted 890 nm infrared light. 

The first LED was patented by Texas Instruments engineers in 1961 and emitted 890 nm of light. It too was the product of an accidental near-infrared discovery by Robert Biard and Gary Pittman. (Image source: Edison Tech Center)

One of the first visible-spectrum LEDs came a very short time after, courtesy of Nick Holonyak, Jr. in late 1962. This LED emitted a red light visible to the human eye via the electroluminescence of a gallium arsenide phosphide (GaAsP) semiconductor. The first commercially available LED lamps launched in 1968 using a variant of this technology, but they were largely unsuccessful because of the manufacturing cost and the deep red color of the light they emitted.

The 1970s: Better and Brighter

In the early 1970s, M. George Craford, a former graduate student under Holonyak, developed his own version of the visible-spectrum LED: one that emitted a yellow light. As if that wasn’t enough, Craford also went on to improve the brightness of red and red-orange LEDs by a factor of 10.

When the first blueish-hued LEDs entered the scene, also in the early 1970s, they didn’t work super well. The first was made at Stanford University with magnesium-doped gallium nitride. Its creators, Herb Maruska, Wally Rhines, and Professor David Stevenson, were awarded the patent in 1972. While magnesium-doping of gallium nitride didn’t produce practical light levels at the time, it is still the basis for all blue commercial LEDs.

A few years later, in 1976, the first high-brightness and high-efficiency LEDs were developed by Thomas P. Pearsall for optical fiber telecommunications using semiconductor materials that were specially adapted to the use case. LEDs continued to gain popularity throughout the 1970s when Fairchild Optoelectrics began producing them at the low cost of five cents per unit.

The 1980s – 1990s: Feeling Blue

What many consider the first commercial success for LEDs came in 1989, when Cree took a blue, silicon-carbide LED to market. The SiC-based LEDs had a very low efficiency level, but who cares? They were blue.

The advent of blue LEDs enabled the creation of what we now see commonly throughout the world: white LEDs, of which there are two types. The first mixes blue LEDs with a yellow fluorescent substance to create a white emission, while the second combines blue, red, and green. Either way, LEDs that emit a white light would not exist today without the hard-earned creation of the blue. 

Blue-emitting LEDs were the final puzzle piece to creating the elusive white-emitting LEDs. (Image source: Instructables)

The 1980s – 1990s, Part 2: Emitting Efficiency

Throughout the ‘80s and into the ‘90s, Isamu Akasaki and Hiroshi Amano, along with Shuji Nakamura, put tons of work and research toward creating a blue LED with brighter light emission. Akasaki and Amano did hundreds of experiments using a metal organic chemical vapor deposition method, and in the early 1990s they found success: a bright blue LED with 1% emission efficiency levels.

Meanwhile, Nakamura had been creating his own versions of blue-emitting LEDs. One was a homo-junction blue-light LED that had a 0.18% light emitting efficiency; the other was a heterostructure type with 0.22% light emitting efficiency, which he later improved to 2.7% efficiency.

We all know that the more efficient an LED, the more power (and money) savings it provides over the long run. Thanks to the efficiencies pioneered by Akasaki, Amano, Nakamura, and others, many of today’s LEDs have lifecycles of around 50,000 hours. If you break that down by years, it’s over a decade of running at 12 hours per day. At 8 hours a day, they can last 17 years.

This lifespan is about 50 times that of incandescent bulbs.

The 2000s: Seeing Temperature in All the Colors of the Rainbow

Even as early as the 2010s, LEDs were already beating incandescent and fluorescent lights in efficiency by a long shot. At that point standard LEDs were operating at around 83 lumens per watt, while fluorescent lamps were at 67 and incandescent lamps were at about 20. But in 2014, experimental white-light LEDs from Cree were found to achieve 303 lumens per watt(!).

As LEDs entrenched themselves as superior technology, other experimental endeavors were underway. Including adjustable color temperatures that are now commonplace.

We know that colors can have different temperatures that are visible to the human eye. White LEDs display this range in color temperature, too, which is why you’re not always stuck with just one color when you turn on a smart light bulb. LEDs measure color temperature in Kelvins. The lower the temperature, the warmer the light’s appearance.

White LEDs can project light in a variety of shades depending on the color temperature, measured in Kelvins. (Image source:  Four Bros Lighting)

Now, obviously LEDs aren’t limited to just emitting varying shades of white. The advancements discussed have allowed LED emissions to encompass basically every color that’s ever existed — and they can do it with just the combination of red, green, and blue. 

Each color is produced by adding different materials like the GaAsP Holonyak used in creating the red LED. And when you combine the three colors and place them into one LED, controlling the intensities of each color can produce millions of different shades.

Lights Are On, No One is Home

LED technological advances have been on a roll for decades. This brings us to a product we all know: smart lightbulbs.

The first smart lightbulbs as we know them today, with color-changing capability and a network connection for wireless control, was the Philips Hue line released in 2012. This system uses – you guessed it – LED lamps, and integrates wireless communications that allows the devices to be cycled on/off or to and from colors remotely.

Philips Hue smart lightbulbs emit warm to cool colors and can be controlled remotely. (Image source: ExtremeTech)

The LED certainly came from humble beginnings, starting off as literally invisible to the human eye and progressing to something we use in our homes to create whatever ambient light we please. In fact, they are as close to ubiquitous as any technology in existence.

So the next time you’re blinded by headache-inducing headlights, just remember, it was an accident.

 

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