An even brighter idea
"Back in the dark ages
The first observation of a semiconductor emitting light when zapped with electricity dates back to 1907. But because the amount of light produced was tiny, no one pursued the idea in earnest. That changed in the early 1960s, when Nick Holonyak, a researcher at General Electric, first learned that semiconductors could generate infra-red light. He then set out to make a new type of semiconductor crystal that would be able to emit visible, red light. He succeeded in 1962, inventing the first practical light-emitting diode.
An LED is based on a combination of two semiconductor materials, called n-type and p-type. The n-type is so called because it contains an excess of negatively charged electrons; the p-type contains an abundance of positively charged "holes" that can accept electrons. At the junction where the two materials meet, electrons pair up with holes to form an area depleted of charge that prevents current from flowing. But applying a large enough voltage causes electrons and holes to flow into the junction from opposite sides. As electrons and holes pair up, each electron gives up energy, which is emitted in the form of light. By changing the composition of the semiconductor materials, it is possible to determine the amount of energy given up by each electron, and hence the light's colour."
http://www.economist.com/science/tq/displayStory.cfm?story_id=7904236
"Back in the dark ages
The first observation of a semiconductor emitting light when zapped with electricity dates back to 1907. But because the amount of light produced was tiny, no one pursued the idea in earnest. That changed in the early 1960s, when Nick Holonyak, a researcher at General Electric, first learned that semiconductors could generate infra-red light. He then set out to make a new type of semiconductor crystal that would be able to emit visible, red light. He succeeded in 1962, inventing the first practical light-emitting diode.
An LED is based on a combination of two semiconductor materials, called n-type and p-type. The n-type is so called because it contains an excess of negatively charged electrons; the p-type contains an abundance of positively charged "holes" that can accept electrons. At the junction where the two materials meet, electrons pair up with holes to form an area depleted of charge that prevents current from flowing. But applying a large enough voltage causes electrons and holes to flow into the junction from opposite sides. As electrons and holes pair up, each electron gives up energy, which is emitted in the form of light. By changing the composition of the semiconductor materials, it is possible to determine the amount of energy given up by each electron, and hence the light's colour."
http://www.economist.com/science/tq/displayStory.cfm?story_id=7904236
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