An incandescence device, usually spheroidal, that converts electrical energy to light (and heat).

Cartoon icon representing an idea.

Also a central ingredient of the LightBulbJoke.

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There's a famous story about the inventor ThomasEdison. Someone came to him wanting a job, so he set a challenge: gave him a light bulb and said "Tell me its volume". So, the would-be employee went away with a set of calipers and a slide rule, and after a while (and a lot of measuring and calculating) he came back and gave an approximate answer. "Let's see", said Edison. He filled the bulb with water, and poured it into a measuring cylinder. "You're about 10% out. Not bad." :-) (I don't vouch for any of the details of this story...)
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A Scottish guy called Joseph Wilson Swan demonstrated working light bulbs 10 years before ThomasEdison did, and got a patent one year before. Then there was a huge court case that Edison lost.
* http://web.archive.org/web/20080602054756/http://www.maxmon.com/1878ad.htm
* http://www.uselessknowledge.com/trivia/explain/docs/edison.asp
* http://www.google.com/search?q=Joseph+Swan+light+bulb
* http://en.wikipedia.org/wiki/Lightbulb
For more details, including some much earlier work:
* http://www.willitsell.com/edisnmth.htm
* http://lightbulb.biography.ms/
* http://home.frognet.net/~ejcov/evans.html
''He wasn't the only one. Edison and the light bulb are simply one in a long, long, line of invention myths. Seems everyone wants a countryman to have credit, facts be damned. What Edison *did* do, was to vastly improve the construction - this is in itself worthy of respect, and tarnished by lying about origins.''

Indeed, Edison's achievements are astonishing and should not be forgotten. What should also not be forgotten is that there were others whose work Edison knew and used. 

Often when someone discovers something others are not present or aware of it, let alone able to use working examples, so the record of inventions is often wrong. Commercial availability is more important historically. It is one thing to produce an experimental result, and quite another to mass-produce an economically viable product. History has identified Edison as the light bulb's inventor because he made it available as a consumer product first. His light bulbs were replicated and continuously manufactured; they were the first used by many thousands. Edison was more a discoverer and implementor than an inventor in the purest sense. It was his SuccessOrientedApproach which provided the means and method to develop products which achieved widespread use. This obviously applies to other discoveries (The invention of Wireless, Work at XeroxParc, for example).
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See AhHa