Tungsten filament light bulb. This device consists of a sealed glass bulb encasing a metal filament (centre, also magnified in background) under an inert gas, usually an argon-nitrogen mixture. Electric current supplied through the connections (bottom centre) flows through the filament, which is made from tungsten. (melting point of 3410 degrees Celsius). The filament heats up and glows as current passes through it, lighting up the surroundings through the glass. Although protected from the oxygen in the atmosphere, the tungsten metal still evaporates, and the filament eventually breaks.