When air touches a light bulb's filament at high temperatures, the filament oxidizes, becoming weak at points. The vacuum in a light bulb acts to prolong the life of the light bulb's filament by keeping it from oxidizing too quickly.
An intact filament is essential to the proper functioning of many types of light bulbs; they need to be strong because bulbs burn out when the filament breaks. The filament's temperature gets very high, generally between 2,000 and 2,550 degrees Celsius.
Tungsten is a metal used in the construction of light bulb filaments. It is used because it has the highest melting point of any metal at 3,420 degrees Celsius.
Instead of vacuums, many light bulbs employ fill gases to help make the filament last longer. Halogen bulbs feature a halogen, such as iodine, that redeposit evaporated tungsten back to the filament.
Despite the benefits associated with fill gases, vacuums are still widely used in many light bulbs. Filaments are operable at higher temperatures with fill gases compared with vacuums, but this reduces the light bulb's efficiency.