Editing Electric light (section)

=== Halogen ===
{{Main|Halogen lamp}}
Halogen lamps are usually much smaller than standard incandescent lamps, because for successful operation a bulb temperature over 200&nbsp;°C is generally necessary. For this reason, most have a bulb of fused silica (quartz) or aluminosilicate glass. This is often sealed inside an additional layer of glass. The outer glass is a safety precaution, to reduce ultraviolet emission and to contain hot glass shards should the inner envelope explode during operation.<ref>{{Cite web |title=Tungsten Halogen – Double Jacket |url=http://www.lamptech.co.uk/TH%20DJ.htm |access-date=2023-03-06 |website=www.lamptech.co.uk}}</ref> Oily residue from [[fingerprint]]s may cause a hot quartz envelope to shatter due to excessive heat buildup at the contamination site.<ref>{{Cite web |title=Should you not touch halogen capsule bulbs with your fingers? |url=https://www.lightingcompany.co.uk/is-it-true-you-should-not-touch-halogen-capsule-bulbs-with-your-fingers-i98 |access-date=2023-03-06 |website=The Lighting Company}}</ref> The risk of burns or fire is also greater with bare bulbs, leading to their prohibition in some places, unless enclosed by the luminaire.

Those designed for 12- or 24-volt operation have compact filaments, useful for good optical control. Also, they have higher efficacies (lumens per watt) and longer lives than non-halogen types. The light output remains almost constant throughout their life.