Why does a lightbulb burn out

health : Why does the lightbulb burn out?

Since the light bulb saw the light of day more than 125 years ago, it has changed considerably. Your filament, for example, is no longer made of coal, but of tungsten. If an electric current flows through the wire, the temperature of the metal rises to 2500 degrees Celsius. It starts to glow and lights up brightly as desired.

Tungsten has the highest melting temperature of all metals. But as soon as it glows white, a tungsten wire also softens. Individual atoms evaporate. They detach from the surface of the filament, deposit on the glass bulb and form a gray film. Over time, the light bulb becomes more and more opaque, the wire thinner and thinner.

After 1000 hours of burning, when the lamp looks pretty black, the filament will eventually burn out. The light would go out much faster if the wire weren't shielded from any air. If oxygen comes into contact with the metal, tungsten will burn at a much lower temperature. In order to protect it from violent reactions with oxygen, the glass bulb of classic lamps is either pumped empty or filled with an inert gas.

With suitable chemical additives in this gas filling, however, the lamp lives much longer, for example with halogen gases such as iodine or bromine. "The tungsten evaporated from the wire forms a chemical bond with the halogen atoms," says Wolfgang Andorfer, product manager for halogen lamps at Osram in Munich. At some distance from the wire, where the temperature is not so high, the two substances combine to form tungsten halide. This circulates in the bulb, and when it reaches the filament again, the tungsten and halogen atoms separate again under the enormous heat. "The tungsten is deposited on the wire again," says Andorfer. Instead of blackening the glass, it is recycled.

However, the cycle is not perfect. The tungsten does not necessarily go back to where it was previously detached from the thread. The wire of the halogen lamp will also burn out at some point. However, halogen lamps have a four times longer service life and also a better light output than conventional light bulbs.

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