Electric light bulb. Filament of an electric light bulb glowing as electricity is passed through it. The filament is a thin wire of a metal with a high melting point, usually tungsten. To prevent the filament oxidising and burning up, it is enclosed in a glass bulb under an inert gas, such as argon. As electricity passes through the filament, the high electrical resistance of the thin metal wire causes it to heat up and give out heat and light. Eventually, the metal in the filament evaporates and the filament breaks, requiring the light bulb to be replaced. Modern light bulbs have improved designs, making them more energy efficient and longer-lasting. The electric light bulb was developed in the 19th century.