Filament in light bulb going from cold to white hot. Bulbs produce light from a filament, a fine tungsten wire which heats up and glows as an electric current is passed through it. Tungsten is an ideal material for a filament, due to its strength and high melting point (3410 degrees Celsius). The interior of the bulb contains an inert gas, usually a mixture of nitrogen and argon. Normal air would corrode the tungsten. While in use, the tungsten filament gradually evaporates away until eventually it breaks.