Why does an incandescent bulb darken over the life of the lamp?
During use, tungsten from the filament evaporates into the gas inside the light bulb. When the tungsten comes in contact with a cool surface it will condense. Often, with incandescent products, the tungsten condenses on the bulb wall, eventually accumulating, and causing darkening of the bulb. Halogen light bulbs eliminate the bulb darkening because halogen light bulbs have a special gas inside their bulb containing halogens. The halogen gas facilitates the “halogen regenerative cycle” which means that the halogens carry the evaporated tungsten back to the filament instead of allowing it to deposit on the bulb wall.
