Editing Incandescent light bulb (section)

===Current and resistance===
The resistance of the filament is temperature dependent. The cold resistance of tungsten-filament lamps is about {{frac|1|15}} the resistance when operating. For example, a 100-watt, 120-volt lamp has a resistance of 144&nbsp;[[ohm]]s when lit, but the cold resistance is much lower (about 9.5&nbsp;ohms).<ref name="GETP110" />{{efn|1=Edison's research team was aware of the large negative [[temperature coefficient of resistance]] of possible lamp filament materials and worked extensively during the period 1878–1879 on devising an automatic regulator or ''ballast'' to stabilize current. It was not until 1879 that it was realized a self-limiting lamp could be built.<ref name="fris10">{{cite book |last1=Friedel |first1=Robert |last2=Israel |first2=Paul |year=2010 |name-list-style=amp |url=https://books.google.com/books?id=8U-Naf4DuzMC&pg=PA26 |title=Edison's Electric Light: The Art of Invention |publisher=The Johns Hopkins University Press |edition=Revised |isbn=978-0-8018-9482-4 |pages=29–31 |access-date=3 July 2018 |url-status=live |archive-url=https://web.archive.org/web/20171206142310/https://books.google.com/books?id=8U-Naf4DuzMC&pg=PA7 |archive-date=6 December 2017}}</ref>}} Since incandescent lamps are resistive loads, simple phase-control [[TRIAC]] [[dimmer]]s can be used to control brightness. Electrical contacts may carry a "T" rating symbol indicating that they are designed to control circuits with the high inrush current characteristic of tungsten lamps. For a 100-watt, 120-volt general-service lamp, the current stabilizes in about 0.10 seconds, and the lamp reaches 90% of its full brightness after about 0.13 seconds.{{sfnp|Friedel|Israel|2010|pp=[https://books.google.com/books?id=8U-Naf4DuzMC&pg=PA22 22–23]}}