Incandescent light bulb

The electric light bulb uses a glowing wire filament heated by electrical resistance to white heat to generate light. The 'bulb' is the glass enclosure which keeps the filament in a vacuum or low-pressure inert gas.

The invention of the light bulb is normally attributed to Thomas Edison in 1879, although some people still see Joseph Swann or even James Bowman Lindsay as the true inventor of the light bulb.

One of the major problems of the standard electric light bulb is evaporation of the filament, leading to narrowing. Where the filament is narrower, electrical resistance is higher (due to the smaller cross-section) and the filament heats up more, increasing the rate of evaporation further at that point. The end point of this process is the failure of the filament.

This problem is addressed in the halogen lamp which is filled with halogen gas. This creates an equilibrium reaction where evaporated filament is chemically re-deposited at the hot-spots, preventing the early failure of the lamp. This allows halogen lamps to be run at higher temperatures which would cause unacceptable low lamp lifetimes in ordinary light bulbs, allowing for greater brightness and efficiency.

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