Editing Halogen lamp (section)

==Effect of voltage on performance==
{{see also|Lamp rerating}}
Tungsten halogen lamps behave in a similar manner to other incandescent lamps when run on a different voltage. However the light output is reported as proportional to <math>V^3</math>, and the [[luminous efficacy]] proportional to <math>V^{1.3}</math>.<ref>Neumann Lichtechnik 1969 21 6 63A</ref> The normal relationship regarding the lifetime is that it is proportional to <math>V^{-14}</math>. For example, a bulb operated at 5% higher than its design voltage would produce about 15% more light, and the [[luminous efficacy]] would be about 6.5% higher, but would be expected to have only half the rated life.

Halogen lamps are manufactured with enough halogen to match the rate of tungsten evaporation at their design voltage. Increasing the applied voltage increases the rate of evaporation, so at some point, there may be insufficient halogen and the lamp goes black. Over-voltage operation is not generally recommended. With a reduced voltage, the evaporation is lower and there may be too much halogen, which can lead to abnormal failure. At much lower voltages, the bulb temperature may be too low to support the halogen cycle, but by this time the evaporation rate is too low for the bulb to blacken significantly. If the bulbs do blacken, it is recommended to run the lamps at the rated voltage to restart the cycle.<ref name="lutron-low-dim">{{cite web |title=Lutron Guide To Dimming Low Voltage Lighting {{!}} Lighting Services Inc |url=http://www.lightingservicesinc.com/about-us/news-events/news/lutron-guide-to-dimming-low-voltage-lighting |website=Lighting Services Inc |language=en |access-date=12 October 2018 |archive-date=7 October 2018 |archive-url=https://web.archive.org/web/20181007223720/http://www.lightingservicesinc.com/about-us/news-events/news/lutron-guide-to-dimming-low-voltage-lighting |url-status=dead }} (Also available as a [http://www.lutron.com/zh-TW/ResourceLibrary/362219.pdf PDF] from lutron.com)</ref> There are many situations where halogen lamps are dimmed successfully. However, lamp life may not be extended as much as predicted. The life span on dimming depends on lamp construction, the halogen additive used, and whether dimming is normally expected for this type.