The development of electricity and of the light bulb are most likely two of mankind's most important achievements, pretty much setting the cornerstone for our modern lifestyles. However, new developments in this field are constantly being made, and probably one of the most important is represented by the LED, or light-emitting diode, which is actually able to provide a fairly OK level of lighting, at the same time requiring a lot less power in order to operate.
LEDs are not as powerful as light bulbs, but their strength relies rather in numbers than individual output. Thus, whenever we're talking about LEDs, it's not very likely to see an individual unit, but a group (or panel) of such minute light sources, that, nevertheless, are quite capable of providing a fairly OK brightness level. Furthermore, LEDs are now being used as light sources in a wide range of displays, such as LCD TVs, laptop displays, etc.
Despite what most people might think, the LED is not exactly a very new discovery, but it has been around, at least at theoretical level, for quite a long time, since it was initially discovered back in the first decade of the 20th century, that golden age of electricity-related discoveries.LED – early development
According to various sources, the first person to experiment and come up with a light-emitting solid-state diode was a British scientist by the name of H. J. Round. However, pretty much in the same time span, Russian researcher Oleg Vladimirovich Losev also published a paper called "Luminous carborundum [silicon carbide] detector and detection with crystals” in the Russian journal “Telegrafiya i Telefoniya bez Provodov” (or Wireless Telegraphy and Telephony), which tackled the same subject.
Unfortunately, the theories were pretty much disregarded at the moment, since the light bulb was too good of an invention then, and the world was rather busy with other matters (like developing weapons for the two world wars). Around 50 years would pass before the LED would make a comeback, and a major one, for that matter.LED – other preliminary experiments
The 1950's brought about a rekindling of the scientific community's interest for the issue of LEDs. For example, back in 1955, Rubin Braunstein, an engineer/researcher working for the Radio Corporation of America, wrote a very detailed study on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys used in simple diode structures. Then, in 1961, two researchers working for Texas Instruments, Bob Biard and Gary Pittman, discovered the fact that that gallium arsenide emitted an infrared radiation when electric current was applied. And even if they were not the first ones to develop an actual working model, Biard and Pittman were able to prove the priority of their work and received the patent for the infrared light-emitting diode.First visible spectrum light-emitting diode
However, the first practical visible-spectrum (red) LED was developed in 1962 by a researched for the General Electric company, Nick Holonyak Jr., who is officially credited as the “father of the light-emitting diode.”
Holonyak, a student of Nobel-prize winner John Bardeen, the developer of the transistor, developed the LED while working for General Electric. Actually, this was pretty much the only breakthrough development he made for GE, because later in his life, he chose the academic path, becoming a researcher and professor at the University of Illinois.
Even if the first working model was developed in 1962, the first LEDs became commercially available in late 1960s, and were red. At the time, they were used as replacements for incandescent indicators, and in seven-segment displays, first in laboratory and electronics test equipment, then in a wider range of home appliances, such as TVs, radios, telephones, calculators, and even watches. Unfortunately, at the time, they were not powerful enough to illuminate a certain area.LEDs through the 1970's – 1980's Early 1970's
Throughout the 1970's, the developments in LED technology led to the appearance of additional colors and wavelengths. The most common materials were GaP green and red, GaAsP orange or high efficiency red and GaAsP yellow, all of which are still used today.
Unfortunately, the reliability of LEDs was still a pretty major issue, mainly due to the fact that LED assemblies were manufactured by hand. This resulted in defects such as "epoxy slop" which caused VF (forward voltage) and VR (reverse voltage) leakage or even shorting of the PN junction. Furthermore, since most of the materials used in LEDs were far from the level of refinement achieved nowadays, the rate of failure was a lot bigger.New developments
The second major leap forward in LED technology occurred in the 1980's, with the development of the GaAlAs (gallium aluminum arsenide) material, which helped LEDs deliver a brightness level ten times bigger than that generated by previous materials. Additionally, the voltage required for operation was lower, resulting in total power savings, and the LEDs could also be easily pulsed or multiplexed.
This new development led to the spreading of LEDs to certain areas previously inaccessible to them, such as bar code scanners, fiber optic data transmission systems and medical equipment. However, the GaAlAs material was still far from being perfect, since it was only available in a red 660nm wavelength, while the light output degradation of GaAlAs was far greater than that of standard technology.
Over the same period, yellow, green and orange LEDs saw only a minor improvement in brightness and efficiency, related mostly to the improvements in crystal growth and optics design, since the basic structure of the material remained relatively unchanged.Laser makes an entrance
In order to overcome some of the issues mentioned above, researchers had to borrow some ideas for a competing technology that was developing quite fast at the time, namely laser diodes. And the first breakthrough was the development towards the end of the 1980's of InGaAlP (Indium Gallium Aluminum Phosphide) visible LEDs, which offered a higher level of versatility as far as the LED's color output was concerned, by adjusting the size of the energy gap. This way, green, yellow, orange and red LEDs all could be produced using the same technology, while the light output degradation level had been significantly improved.Other developments in LED technology
The first experiments regarding blue LEDs occurred back in the 1970's and were conducted by Jacques Pankove (inventor of the gallium nitride LED) at RCA Laboratories, but the results were not exactly fantastic. Research related to blue LEDs continued and, in the late 1980's, some key breakthroughs in GaN epitaxial growth and p-type doping were achieved by Isamu Akasaki and Hiroshi Amano, who worked for the University of Nagoya, in Japan.
Following in the footsteps of the two researchers mentioned above, in 1993, Shuji Nakamura of Nichia Corporation of Japan demonstrated the first high-brightness blue LED based on InGaN. Then, in 1995, Alberto Barbieri from the Cardiff University Laboratory in the United Kingdom investigated the efficiency and reliability of high-brightness LEDs, demonstrating very high results by using a transparent contact made of indium tin oxide (ITO) on (AlGaInP/GaAs) LED. These developments led to the appearance of the first white LED.
Over the course of the 1990's and 2000's, the popularity and range of uses of LEDs have virtually skyrocketed, the small light-emitting diodes being used in a wide variety of products, for actually providing some light, as light sources for LCDs and laptop panels, and much more. Nowadays, a LED could be found just about anywhere a light source is present, and things are most likely going to evolve even further.The future of LEDs
Right now, the future of LEDs seems to be a pretty bright one, since light-emitting diodes are universally regarded as the evolution of lighting solutions, mainly due to their energy efficiency. Research in the area is constantly being carried out, and it will certainly translate into even more powerful, long-lasting and low-energy consuming products.