December 20

An incandescent light bulb, incandescent lamp, or incandescent light globe is a type of electric light that uses a wire filament that is heated until it lights. To protect the filament from oxidation, it is encased in a glass bulb with a vacuum or inert gas. The filament was the source of the difficulty with Swan's design, Edison understood. A thin filament with a high electrical resistance would make a lamp feasible since it would only take a little amount of electricity to light up. In December 1879, he displayed his lightbulb.
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