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The history of light-emitting diodes follows the growth of a technological idea in optical communications. Today we have nearly ubiquitous LED lights, but for decades they did not exist as they do today while scientists and engineers worked to solve the problems that gave rise to them today. It’s about our imaginations going beyond what is currently available. We continue to build on it and grow it. In some ways this has been good, in many ways not so good. It’s not the technology to blame, however, it is our response to it and, I truly believe, that it’s just too much too soon for our systems and our intelligence at this time. Given time and effort, may this change.

 

What is a light-emitting diode?

As an introduction to a short history of light-emitting diodes or LEDs, let’s look at what it is. An LED or light-emitting diode is a two-lead semiconductor light source. it uses a p-n junction diode that emits light when activated. All those electrons are combining with electron holes in the LED, releasing out as photons. This is called electroluminessence. The CL or color of the light is determined by measurement of the energy band gap of the semiconductor. Simple, right? You’ve got 2 leads with a basic on off junction. On, the light comes on, off, the light goes off.

Early LEDs were mainly used commercially in infrared applications and in electronic device indicator lamps. Advantages over incandescent are energy savings, longer life, improved physical structure, smaller size and faster switching. They are being used more and more in a majority of new lighting installations, including home light bulbs. LEDs also currently have no red flags about disposal as the short-lived CFLs have. I have a pile in my basement, I’m still not sure what to do with.

History of Light-emitting diodes

Electroluminessence is discovered in 1907 by British experimenter H.J. Round of Marconi Labs. The materials he used were a crystal of silicon carbide and a cat’s-whisker detector. This is sometimes called a crystal detector, which was discovered in 1874 by Karl Ferdinand Braun. A thin wire lightly touched a crystal of semiconducting material to create an asymmetric conduction. First application was for early crystal radios and continued in use through WWII.

In 1927 Oleg Losev, a Russian inventor, reported the creation of the very first LED. Even though his research and findings were distributed to Soviet, German and British scientists, no practical use was made for several decades. Until 1951, when a group of scientists, including Kurt Lehovec from Bohemia in the Czech Republic, explained the first LEDs using silicon carbide (SIC) with current from a battery. Two years later, in 1953, they compared this to a variant, pure crystal to further refine the technology.

History of Light-emitting diodes – RCA and Optical Communications

Rubin Braunstein with RCA (Radio Corporation of America) in 1955 experimented with other semiconductor alloys. During the year 1957, he demonstrated that rudimentary devices could be used for non-radio communication across short distance. He “…had set up a simple optical communications link: Music emerging from a record player was used via suitable electronics to modulate the forward current of a GaAs diode. The emitted light was detected by a PbS diode some distance away. This signal was fed into an audio amplifier and played back by a loudspeaker. Intercepting the beam stopped the music. We had a great deal of fun playing with this setup.”  This experiement was an early advancement towards LED use in optical communications.

Gallium Arsenide Substrate

Things began heating up in 1963. James R. Biard and Gary Pittman, working at Texas Instruments, discovered near-infrared (900 nm) light emission from a tunnel diode they made on a gallium arsenide (GaAs) substrate. This was the same alloy used by Braunstein in 1957. In 1962 they filed a patent titled “Semiconductor Raadiant Diode.” The paper described a “zinc diffused p–n junction LED with a spaced cathode contact to allow for efficient emission of infrared light under forward bias.“ A p-n junction is, again, the on-off switch. Texas Instruments got the patent a year later after establishing that their research pre-dated that of GE Labs, RCA Research Labs, IBM Research Labs, Bell Labs, and finally Lincoln Lab at MIT.  In the same year, the first visible-spectrum (red) LED was developed by Nick Holonyak, Jr. at General Electric, which was published in the Applied Physics Letters journal on Dec. 1, 1962.

LEDs and Optical Fiber Communications

10 years later in 1972, M. George Craford, a former grad student of Holonyak at Texas Instruments, invented the first yellow LED. His work also improved the brightness of the red and red-orange LEDs by a factor of 10. The first high brightness and high efficiency  LEDs were introduced in 1976 by T.P. Pearsall in his work for optical fiber telecommunications. He created materials specifically adapted to optical fiber transmission wavelengths. In the early 2000’s I worked as a systems admin and spent many joyous hours pulling fiber cable under the floors of the data center, remembering the early warning from one of my co-workers not to look directly into the cable. Yes, indeed.

History of Light-emitting diodes – Blue LEDs and Gallium Nitride

Still in 1972, blue LEDs were developed by Herbert P. Maruska at RCA using gallium nitride (GaN) on a sapphire substrate. They were first sold in the US by a company named Cree in 1989, but they were blue and they were not very bright. In 1994, Shuji Nakamura of Nichia Corp used Indium gallium nitride (InGaN), achieving the first high-brightness blue LED. At the same time, Isamu Akasaki and Hiroshi Amano in Nagoya were experimenting with a very hard crystal, gallium nitride (GaN). This completed the range of primary colors, opening the door for daylight visible full color LED displays and blue laser devices. All three of these scientists received the Nobel prize in Physics in 2014.

In 1995, a ‘transparent contact’ was demonstrated by Alberto Barbieri at the Cardiff University Lab using indium tin oxide (ITO) on (AlGaInP/GaAs). You may need to be a physicist to understand that one, but there it is. Suffice it to say, the race was on for an LED technology that worked to replace the incandescents that needed to go away and the CFLs that were increasingly problematic.

History of Light-emitting diodes – Gallium Nitride on silicon successful

2001 and 2002 we’re growing gallium nitride (GaN) on silicon successfully. in January 2012, Osram Licht AG, a multinational lighting manufacturer headquartered in Munich, Germany, began the first commercial applications using high-power InGaN LEDs grown on silicon substrates. Plessy Semiconductors, located in Plymouth, England with its “state of the art 270,000 square foot semiconductor facility that includes Gallium Nitride (GaN) on silicon growth capacity,” have also been leaders in early commercial adoption and research. They’ve been around for over 100 years, although weathering many changes.

The first white LED lights were inefficient and expensive. Using the yellow light (through fluorescence) with the blue appears white to our eyes. The light output continues to increase exponentially, with a doubling of light occuring approximately every 36 months. Companies involved now in the manufacture of LEDs include Panasonic, Nichia, Samsung, Solstice, Kingsun and many countless others.

Light-emitting diodes – Moving forward

As the cost falls and we humans buy more and more of them and make our nights brighter and brigher yet, we are most certainly at risk of lighting our nights too much, way too much… and we are already seeing signs of this happening very quickly. We need to slow this down so that we don’t morph into some 24 hour work cat. If you are interested, take a look at http://www.darksky.org/eyes-in-the-sky-exploring-global-light-pollution-with-satellite-maps/ This is where these Milan photos were sourced.

The city center became noticeably more blue in the interim after the Milan converted much of its municipally-owned lighting from low-pressure sodium vapor lamps to white LED lamps.

Milan before LED (2012) and after LED was installed (2015). According to the IDA, “the city center became noticeably more blue in the interim after the Milan converted much of its municipally-owned lighting from low-pressure sodium vapor lamps to white LED lamps.”

Based on the previous record of discoveries and inventions around LEDs, I am confident that we will see an improvement. However, an improvement on the scale I am imagining, that is, warmer, softer, and less light than we seem to feel we require now, will take changes of habits, changes of perceptions. That is, we are humans, we have a circadian rhythm. We share the earth with birds and insects, reptiles, fish, and other animals, all who are suffering from our over use of lighting. Whether it’s LED or some other technology, that should be our goal.

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