Argon gas is used in fluorescent and incandescent light bulbs to stop the oxygen in the light bulbs from corroding the hot tungsten filament. The use of argon in light bulbs prevents the evaporation of the tungsten filaments, which results in increased light bulb life.
Argon is an inert gas, and hence would not react with the tungsten filament. The bulb needs a gas in it instead of a vacuum because a vacuum would encourage oxygen to come in from the exterior.
