10 Interesting Facts About LEDs
1. “A curious phenomenon” is what HJ Round reported in 1907, when he applied a voltage to a crystal of carborundum (silicon carbide, SiC), which in turn “gave out a yellowish light”. This was the first official report of electroluminescence – light emission from a solid-state material directly caused by an electrical power
2. The first visible LED was invented in 1962 by Professor Nick Holonyak who then worked for General Electric
3. Light bulbs shine by incandescence (emitting light as a result of being heated), LEDs by electroluminescence (luminescence produced electrically, especially by the application of voltage)
4. LEDs are driven by DC (direct current), light bulbs are driven by AC (alternating current)
5. LEDs don’t attract as many insects as other traditional light sources as they have very little UV content
6. LEDs are great for horticulture – deep blue (450nm) and hyper red (660nm) provide the light for photosynthesis, and far red (730nm) controls the plant from germination to vegetative growth and flowering.
7. Good quality LEDs (such as Osram) can easily have a lifetime which exceeds 50,000 hours
8. More and more councils changing over their streetlights to LED versions, saving energy and increasing visibility.
9. Blue LEDs can help keep food fresh - they have been proved to have a strong antibacterial effect on major foodborne pathogens, and are now being used in fridges.
10. The Times Square Ball in New York (dropped every New Year) is illuminated with 32,256 individual LEDs!
1st Image- "Carbonfilament" by Ulfbastel - Own work (own photo). Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Carbonfilament.jpg#/media/File:Carbonfilament.jpg
2nd image - By Vaishak Kallore (Vaishak Kallore) (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
5th Image - By Susan Serra, CKD from Long Island, USA (222 (2)) [CC BY-SA 2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons
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Article says LEDs have a lifetime of over 50,000 hours? Far more, I'd say. In 1975 I built a digital clock made of red LEDs (7-segment type) and it has been running ever since almost without interruption. That's 44 years or around 380,000 hours and they are all still going strong. So, with production improvements nowadays, it's quite likely that we're looking at LEDs that could last a lifetime - literally.
@Philinengland I think this is primarily aimed at higher power LEDs which typically have a stated life around 50k hours or more. Generally you'll see this stated as an L70 life of 50k hours meaning 70% of the initial brightness (lumens) is maintained for 50k operating hours. In some cases this is with LEDs running with a driving current of over 1 Amp. I worked in lighting for a while during the transition to LED light sources and it was a very interesting time. The work that the lighting majors such as Osram, Philips and Tridonic put into product quality and reliability was impressive. The first LED spot light I worked on was designed for 50k hours but last I heard the predicted life of the spot (samples on continuous stress test since manufacture) was around 360k hours. You could say we did too good a job as although it was way more efficient than say Halogen with a total system efficacy or around 65 lm/watt. Only four years later we were able to deliver the same light quality in a smaller and lower cost product with an efficacy of better than 100 lm/watt.
Minaev - Many thanks for your information on O V Losev. It was not a name we were aware of, but with further research we realise the importance of his work. In an article such as this it is difficult to cover all aspects of such inventions. We mentioned Nick Holonyak as he was the first to make a product that the general public would recognise as being like the LED technology.
Museamcurator - Thanks for your comment – yes indeed light bulbs can be driven by a DC current. In articles such as these it is difficult to go into much detail, so we used a generalist approach where 90%+ of light bulbs will be driven by AC current.
Mistakes. The first LED was invented in the Soviet Union, but the inventor is not able to develop the idea, because he died in action during World War II. OV Losev in 1923, when he was experimenting with a rectifying contact of a pair of "silicon carbide - steel wire," found at the point of contact between two dissimilar materials faint glow - semiconductor junction electroluminescence (at that time the concept of "semiconductor junction" did not exist yet ). This observation was published, but the weighty significance of this observation has not been understood and has not been studied for decades. The intensity of the observed radiation was so small that the Russian scientific community if seriously interested in this phenomenon. Five years later, Losev is specially engaged in research of this effect and continued until near the end of their life (OV Losev died in the siege of Leningrad in January 1942, before the age of 39 years). Opening «Losev Licht» (light Losev) is named effect in Germany, where Losev published in scientific journals, has become a worldwide sensation. After the invention of the transistor in 1948 and the creation of the theory of pn-junction (the basis of all semiconductors) became clear the nature of luminescence. Thus, the opening Losev consolidated leadership in the area of ??the USSR.