Editing Incandescent light bulb (section)

===Coiled coil filament===
To improve the efficiency of the lamp, the filament usually consists of multiple coils of coiled fine wire, also known as a '''''coiled coil'''''. Light bulbs using coiled coil filaments are sometimes referred to as 'double-coil bulbs'. For a 60-watt 120-volt lamp, the uncoiled length of the tungsten filament is usually {{convert|22.8|in|order=flip}},<ref name="GETP110" /> and the filament diameter is {{convert|0.0018|in|order=flip}}. The advantage of the coiled coil is that evaporation of the tungsten filament is at the rate of a tungsten cylinder having a diameter equal to that of the coiled coil. The coiled-coil filament evaporates more slowly than a straight filament of the same surface area and light-emitting power. As a result, the filament can then run hotter, which results in a more efficient light source while lasting longer than a straight filament at the same temperature.

Manufacturers designate different forms of lamp filament with an alphanumeric code.<ref>Donald G. Fink, H. Wayne Beatty, ''Standard Handbook for Electrical Engineers, Eleventh Edition'', McGraw Hill, 1978 {{ISBN|0-07-020974-X}}, page 22-5</ref>

{{stack|
[[File:filament.jpg|thumb|Coiled coil filament of a 200-watt incandescent lightbulb highly magnified]]
[[File:Fused Electrical Filament SEM Stereo 50x.JPG|thumb|Filament of a burnt-out 50-watt incandescent lightbulb in an [[Scanning electron microscope|SEM]] in stereoscopic mode, presented as an [[anaglyph image]].{{3D glasses}}]]
[[File:Fused Electrical Filament SEM Stereo 500x.JPG|thumb|Filament of a 50-watt incandescent lightbulb in an [[Scanning electron microscope|SEM]] in stereoscopic mode, presented as an [[anaglyph image]].{{3D glasses}}]]
}}

Electrical filaments are also used in [[hot cathode]]s of [[fluorescent lamp]]s and [[vacuum tube]]s as a source of [[electron]]s or in vacuum tubes to heat an electron-emitting electrode. When used as a source of electrons, they may have a special coating that increases electron production.