bild

Light bulb. View of an electric light bulb. Bulbs produce light from a filament (at centre), a fine coiled wire of tungsten which heats up and glows as an electric current is passed through it. Tungsten is an ideal material for a filament as it is strong and has a 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 corrode the tungsten. Whilst in use, the tungsten filament gradually evaporates away until eventually it breaks. (KEYSTONE/SCIENCE PHOTO LIBRARY/CORDELIA MOLLOY)