Some light bulbs are filled with gas. The type of gas can vary depending on the type of light bulb. As the filament burns, tungsten particles separate from the filament, eventually causing the filament to weaken and break. The presence of gas inside the light bulb helps extend the lifespan of the light bulb by slowing the evaporation process of the tungsten.

Originally, there was no gas inside of a traditional light bulb. Instead, a vacuum was created to allow air to oxidize the filament when heated. However it was discovered that gas atoms can "bounce" tungsten atoms back onto the filament, restoring the filament structure.

There are a few types of gases that can be found in a light bulb. Usually only one type of gas is found in a single bulb. The first type of gas used, and one found in common incandescent bulbs, is argon. Sometimes the argon gas is mixed with nitrogen. Some light bulbs contain halogen or xenon gas. Krypton gas is also found in some light bulbs.

Besides helping to slow the evaporation of tungsten from the filament, each gas has a slightly different benefit during use. Krypton- and xenon-filled light bulbs do not burn as hot as argon-filled ones.

These types of gases also have larger atoms than argon gas, making them more effective at bouncing tungsten atoms back to the light filament. This in turn results in longer-lasting light bulbs.

Halogen light bulbs last longer than the other types of gas-filled bulbs, with a lifespan of up to three years or about 2,500 hours of use.

Mercury is found in fluorescent light bulbs, but it is not in gas form. Rather, the inside of these bulbs is coated with a mercury powder that aids in the light production process.

Also, while krypton- and xenon-gas-filled bulbs tend to put off less heat than those filled with argon, halogen light bulbs run extremely hot, upward of 250 degrees C or 482 degrees F. A 300-watt halogen bulb can easily reach temperatures of 300 degrees C or higher.

Other types of light bulb technology, such as LED lights, do not contain gases; incandescent bulbs that contain a coated filament are the primary types that contain some form of gas.

The cost of xenon, krypton and halogen light bulbs is higher than argon-filled bulbs. According to the "The Great Internet Light Bulb Book," xenon gas is the best choice but also the most expensive to use.

Another consideration is the safety associated with certain gas-filled bulbs. Halogen bulbs not only run extremely hot, but their glass also can become weakened when touched because of the oil in our skin.