Why does a halogen light bulb last longer than a regular incandescent bulb?

Both regular incandescent bulbs and halogen bulbs create light by heating a filament (made of tungsten) inside the bulb; the heat makes the filament white-hot, producing the light that you see. Usually, the bulb burns out when the filament wears out.

The filament on a regular incandescent bulb wears out over time because the tungsten on the filament evaporates and is redeposited on the bulb's glass. (This is also why bulbs often appear darker when they burn out; what you're seeing is tungsten deposits on the inside of the glass.) Halogen bulbs last longer because the halogen gas inside the bulbs redeposits the tungsten back onto the filament as it evaporates. A halogen bulb will still eventually burn out, because the tungsten isn't redeposited evenly on the filament, and the filament will eventually develop a weak spot. Even so, halogen bulb technology is a great improvement over regular bulbs — they last around 4 times longer while providing a superior quality of light.

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