Why do halogen light bulbs last longer?
Hot-burning "halogen bulbs" can last two or three times longer than regular bulbs because they are filled with chemically active halogen gases that preserve the filament.
The filament of an ordinary light bulb burns out because atoms of tungsten evaporate from its surface, so that it becomes thinner and thinner until it breaks. The evaporated tungsten is deposited on the inside surface of the bulb, where it forms a dark deposit.
The gas inside a halogen bulb combines with the tungsten atoms that condense on the glass, removing the deposit. When the combined molecules touch the hot filament, the tungsten is redeposited there, and the gas is released to do the same trick again.
A halogen bulb is often 10 to 20 percent more efficient than an ordinary incandescent bulb of similar voltage, wattage, and life expectancy. Halogen bulbs may also have two to three times as long a lifetime as ordinary bulbs, sometimes also with an improvement in efficiency of up to 10 percent.
incandescent bulb: 白炽灯泡