Electric light bulb. Closeup of a glowing tungsten filament in an electric light bulb. Light bulbs produce light from a filament (fine coiled wire) that heats up and glows as an electric current is passed through it. Tungsten is used 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. Air cannot be used as the oxygen it contains would cause the tungsten to burn up immediately. Whilst in use, the tungsten filament gradually evaporates until eventually it breaks and the bulb must be replaced.