Light bulb filament is made of tungsten metal. Power applied, the filament heating temperature reaches above 2500 ℃. Sublimation of tungsten at high temperatures, some tungsten filament particles did give the surface came out, settling on the bulb wall. Over time, black light bulbs will reduce the brightness and lighting effects.
Scientists are down and the gas flow characteristics of the movement, in the light bulb on a small amount of inert gas-filled, and the light bulb made of pear. This inert gas flow inside the bulb, the tungsten evaporation largely black particles to the gas volume above the sediment in the neck bulb, light bulb around and can reduce the impact of the bottom, to keep the glass transparent, so that bulb is not affected.