Why do halogen bulbs last longer than ordinary incandescent bulbs?

Halogen bulbs last longer than ordinary incandescent lamps due to a chemical process known as the halogen cycle.12

In a standard incandescent bulb, the tungsten filament evaporates during operation, which eventually leads to the filament breaking and the bulb darkening as tungsten condenses on the glass.1

In contrast, halogen bulbs contain a small amount of a halogen element, such as bromine, alongside a noble gas. When tungsten evaporates from the hot filament, it reacts with the halogen gas to form a compound. This compound is then attracted back to the filament, where it decomposes and redeposits the tungsten. This cycle effectively repairs the filament and prevents the tungsten from darkening the bulb, thereby extending the life of the lamp.21