Editing Incandescent light bulb (section)

==== Metal filament, inert gas ====
[[File:Squirrel Cage filament lamp.jpg|thumb|upright|A tantalum lamp with a 1 meter long filament.]]

US575002A patent on 01.Dec.1897 to Alexander Lodyguine (Lodygin, Russia) describes filament made of rare metals, amongst them was tungsten. Lodygin invented a process where rare metals such as tungsten can be chemically treated and heat-vaporized onto an electrically heated thread-like wire (platinum, carbon, gold) acting as a temporary base or skeletal form. (US patent 575,002). Lodygin later sold the patent rights to GE.

In 1902, [[Siemens]] developed a [[tantalum]] lamp filament that was more efficient than even graphitized carbon filaments since they could operate at higher temperature. Since tantalum metal has a lower resistivity than carbon, the tantalum lamp filament was quite long and required multiple internal supports. The metal filament gradually shortened in use; the filaments were installed with large slack loops. Lamps used for several hundred hours became quite fragile.<ref>I. C. S. Reference Library Volume 4B, Scranton, [[International Textbook Company]], 1908, no ISBN</ref> Metal filaments had the property of breaking and re-welding, though this would usually decrease resistance and shorten the life of the filament. General Electric bought the rights to use tantalum filaments and produced them in the US until 1913.<ref>{{cite web|title=GE Tantalum Filament 25W of American Design|url=http://www.lamptech.co.uk/Spec%20Sheets/IN%20TA%20GE%2025W.htm|publisher=Museum of Electric Lamp Technology|access-date=17 June 2013|url-status=live|archive-url=https://web.archive.org/web/20121113175731/http://www.lamptech.co.uk/Spec%20Sheets/IN%20TA%20GE%2025W.htm|archive-date=13 November 2012}}</ref>

From 1898 to around 1905, [[osmium]] was also used as a filament in lamps made by [[Carl Auer von Welsbach]]. The metal was so expensive that used lamps could be returned for partial credit.<ref>{{cite web|url=http://home.frognet.net/~ejcov/osmium.html|title=The Osmium Filament Lamp|work=frognet.net |url-status=dead|archive-url=https://web.archive.org/web/20081012030517/http://home.frognet.net/~ejcov/osmium.html |archive-date=12 October 2008}}</ref> It could not be made for 110&nbsp;V or 220&nbsp;V so several lamps were wired in series for use on standard voltage circuits. These were primarily sold in Europe.