led-safety.co.uk ebook on history of led
Light-emitting diodes (leds) were an accidental discovery at first.
At the beginning of the 20th century, it was discovered that when electricity was applied to the semiconductor silicon carbide (sic) it produced a light. This light was too dim to be of any use so the research was never distributed. This could have been the end for the led, but it wasn t content to die out.
Nearly 20 years later russian and german scientists revisited the idea of light produced this way. The light was still of such poor luminance that the idea nearly died again. A report published in 1936, which helped to invent the term electroluminescence, revived the research for light from this source.
The science of electroluminescence languished in obscurity for a while. It began to gain favor again in the 1950s when some british scientists started experimenting with it again. This led to the first infrared led. From this technology came the first visible spectrum led, in red, from gallium phosphide (gap).
This was the start of the led revolution. From that point each decade brought advances in the technology of light-emitting diodes. The use of different substrates brought brighter lights of different colors. The colors advanced from red to orange and on to pale green, then yellow and on to a brighter green.
By the 1990s the use of gallium nitride helped usher in the era of blue leds. These blue lights became the basis for white light. The use of fluorescent phosphors helped change that blue light into high intensity white lights. Now leds can be found in almost every visible color of light.
This technology has led to additional uses for the led as well. Due to their low light output they started out in indicator lights and display light applications only. The cost of materials was an issue at first and, therefore, they were used only in expensive laboratory and test equipment.
They later began to be used in appliances, calculators and watches