A View From Behind The Meter
History Of LED Lighting
The emergence of LED technology is becoming more and more a part of our everyday lives and it comes to mind that few people have any awareness of how it all started. I think that that the majority of us believe that this is a new technology but that is far from the case. It really goes back over a hundred years to the beginning of the 20th century when a British Marconi engineer by the name of Henry Joseph Round noticed that semiconductors produced light. He wrote a few paragraphs on the phenomenon and made no further investigations. Without any information of Rounds observances twenty years later, a Russian radio technician Oleg Losev living in Novgorad Russia noticed that the diodes used in radio receivers emitted light when current was passed through them. He published the details in a Russian journal at the time and went on to publish his discoveries in 16 journals both in German and British periodicals between 1924 and 1930. Due to these publications Losev could respectively be considered the discoverer of LED technology. The Soviet Union during the following years was embroiled in a turbulent social change culminating in the catastrophic slaughter of World War II and Losev was one of the millions of victims of that period of history. It is believed he died, in the siege of Leningrad by the German Army, of all things starvation in the year 1942 at the young age of 38. It is not known where he was buried.
During the years between 1927 and 1942 Losev theorized correctly that the light was not caused by thermal effects but instead a “cold” light in a new field of science we now call quantum mechanics. No practical usage of the observed phenomenon happened for several decades and at RCA in the United States during the early 50’s Rubin Braunstein reported on infrared emission from gallium arsenide (GaAs). These observances were utilized and developed by two experimenters at Texas Instruments and they applied and received the first patents on infrared LED’s in 1961. The next year in 1962, the first practical visible-spectrum (red) LED was developed by Nick Holonyak Jr. while working at General Electric. Holonyak is considered the “father of visible light-emitting diode technology” by many. Both he and one of his former graduate students, a George Craford, worked to develop red and yellow LEDs. Craford went on to create a brighter, (almost 10 times) red and red-orange LED by 1972. In 1976, T.P. Pearsall created the first high-brightness, high efficiency LED for optical fiber telecommunication.
The first commercial LEDs were commonly used as replacements for incandescent and neon indicator lamps in expensive equipment such as laboratory and electronics test equipment. Until 1968, visible LEDs were very expensive, almost $200.00 per unit. Monsanto was the first to mass-produce visible red LEDs by using the compound gallium arsenide phosphide (GaAaP) which was suitable for indicators usually in test equipment and appliances. Everything changed in the seventies when Fairchild produced LEDs at a cost of less than five cents per unit. The methods used by Fairchild are still being employed by LED manufacturers today. The methods they employed allowed an inexpensive production of light, the brightness of which grew dramatically over the next twenty years, and the devices developed with this technology exploded into the marketplace. Calculator readouts, auto dash display lights, appliance signal lights, proliferated using these efficient long lasting illumination systems. The light output has doubled approximately every six months since 1960 and this trend will seemingly continue as engineers experiment with chemicals to increase output and color in the basic compound substructure. By the late 1980’s LEDs had become common in our daily life but the white light equivalent of incandescent systems had not yet been developed and wouldn’t be until the early 1990’s by an employee of Nichia Corporation in 1994.
Shuji Nakamura graduated from the University of Tokushima in 1977 and joined the Nichia Corporation where he invented the first high brightness gallium nitride LED whose brilliant blue light when converted to yellow by a phosphor coating produces a white light. Nakamura managed to develop a thermal annealing method of irradiating GaN that was suitable for mass production inexpensively. He is responsible for creating the white LED in the early 1990’s as well as the blue laser diodes used in blu-ray discs. In 2014 he was honored with the Nobel Prize in physics together with Prof. Hiroshi Amano for inventing blue light-emitting diodes. This discovery has led to lighting that is viable for our media and inexpensive for an illumination that is for all practical purposes without substantial heat and dramatically less in amperage draw. Nakamura by the way received in 2005 the largest bonus ever awarded to that date paid by a Japanese company, 9 million dollars. He now teaches at University of California Santa Barbara and holds over 100 patents.
Now that we have some idea how we got here, just how does the LED work/?, I’ll try to simplify a very complex physics lesson so that you as technicians understand the nature of what’s happening and can realize the potential of this new efficient source of light. A light emitting diode is a semiconductor light source. A diode can be viewed as an electronic version of a check valve. Electric current is only allowed to pass in one direction (commonly called forward direction) and is used to convert alternating current to direct current. The semiconductor diodes current to voltage characteristics can be tailored for special purposes, light being only one, by varying the inherent materials and introducing impurities into the compound elements or what’s called doping. When a light-emitting diode is turned on (forward based) electrons are able to move from one element to the other and that movement creates a loss of energy in the electrons which in turn creates a photon. This effect is called electroluminescence and the color of the light is determined by the energy gap of the semiconductor. More simply put, introducing DC current to the compound forces a drop in energy in the electrons as the current passes through both elements and the production of a photon is the resulting consequence. Presently our white light is really a blue LED covered with a phosphor coating producing a light that appears white.
(The Cineroid LM400-VCDS Variable Color LED Light displayed above)
The above simplicity is designed to clear the detailed science of the process so that the guy in the trenches can work with a basic understanding of what’s really happening. Trying to convert physics into layman’s terms is very difficult and I hope the above brief description achieves that purpose. As lighting technicians and film makers we will be using LEDs as our primary source of light for the foreseeable future and it is good to know how it operates. Good luck!
-Michael Rogers, Lighting Consultant & Educational Outreach