Why do incandescent bulbs darken over their life?
During the operation of incandescent light bulbs, 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. Over time, tungsten will accumulate on the walls of the bulb and cause 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.
