An electrical filament is a thread of metal, usually tungsten, which is used to convert electricity into light in incandescent light bulbs (as developed in 1874 by Alexander Lodygin and in 1878 by Joseph Wilson Swan, among others), and into heat in vacuum tube devices.

Filament of a 200 watt incandescent lightbulb highly magnified
Filament of a 50 watt incandescent lightbulb in the SEM in stereoscopic / anaglyph mode, magnification 50x
Filament of a 50 watt incandescent lightbulb in the SEM in stereoscopic / anaglyph mode, magnification 200x
Filament of a 50 watt incandescent lightbulb in the SEM in stereoscopic / anaglyph mode, magnification 500x.
Filament of a 50 watt incandescent lightbulb in the SEM in stereoscopic / anaglyph mode, magnification 2000x. The whole surface is covered with re-crystallized metal.

The first successful light bulb filaments were made of carbon (from bamboo), later replaced with tungsten.

[edit] Explanation

An electrical current travels through the filament and as a cause of the electrical resistance of the filament makes it white-hot and generates light and heat. It is always inside a glass enclosure filled with a vacuum or a noble gas or inert gas to stop oxidation. Small amounts of a halogen can be added to facilitate transport and evaporated tungsten atoms back to the filament, resulting in significantly prolonged lifetime when used at higher temperatures, which is exploited in halogen lamps. Electrical filaments are used in hot cathodes of various types of vacuum tubes and electron guns as sources of electrons.

[edit] Types of filament

There are several different types of filament configuration available and it all depends on the lamp itself, and what characteristics are required. Some of these include but are not limited to C-6, CC-6, C-2V, CC-2V, C-8, CC-88, C-2F, CC-2F, C-Bar, C-Bar-6, C-8I, C-2R, CC-2R, and Axial.

[edit] External links

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