Editing Headlamp (section)

==== Disadvantages ====

===== Glare =====
Vehicles equipped with HID headlamps (except motorcycles) are required by [[World Forum for Harmonization of Vehicle Regulations|ECE regulation 48]] also to be equipped with [[headlamp lens cleaning system]]s and automatic beam leveling control. Both of these measures are intended to reduce the tendency for high-output headlamps to cause high levels of [[Glare (vision)|glare]] to other road users. In North America, ECE R48 does not apply and while lens cleaners and beam levelers are permitted, they are not required;<ref>{{cite web |url=http://www.motivemag.com/pub/feature/tech/Motive_Tech_The_Difference_Between_US_and_European_Lights.shtml |title=The Difference Between US and European Lights |website=Motivemag.com |access-date=2010-12-29 |url-status=dead |archive-url=https://web.archive.org/web/20090501102913/http://www.motivemag.com/pub/feature/tech/Motive_Tech_The_Difference_Between_US_and_European_Lights.shtml |archive-date=1 May 2009 }}</ref> HID headlamps are markedly less prevalent in the US, where they have produced significant glare complaints.<ref name="NHTSA_8885"/> Scientific study of headlamp glare has shown that for any given intensity level, the light from HID headlamps is 40% more glaring than the light from tungsten-halogen headlamps.<ref name=Vanderlofske>{{cite web |url=http://www.nhtsa.gov/DOT/NHTSA/NVS/Public%20Meetings/Presentations/2004%20Meetings/VanDerlofske.pdf |title=What Is Glare? p. 24 |website=Webcitation.org |access-date=2012-01-31 |url-status=dead |archive-url= https://web.archive.org/web/20111021132641/http://www.nhtsa.gov/DOT/NHTSA/NVS/Public%20Meetings/Presentations/2004%20Meetings/VanDerlofske.pdf |archive-date=21 October 2011}}</ref>

===== Mercury content =====
HID headlamp bulb types D1R, D1S, D2R, D2S and 9500 contain the toxic [[heavy metals|heavy metal]] [[mercury (element)|mercury]]. The disposal of mercury-containing vehicle parts is increasingly regulated throughout the world, for example under [https://web.archive.org/web/20101229225232/http://www.epa.gov/epawaste/hazard/wastetypes/universal/lamps/index.htm US EPA regulations]. Newer HID bulb designs D3R, D3S, D4R, and D4S which are in production since 2004 contain no mercury,<ref>{{cite web |url=http://www2.prnewswire.com/cgi-bin/stories.pl?ACCT=105&STORY=/www/story/07-27-2004/0002218858 |title=KOITO and DENSO Develop World's First Mercury-Free High-Intensity Discharge Headlamp System |website=Prnewswire.com |access-date=2010-12-29 |url-status=dead |archive-url=https://web.archive.org/web/20210308004434/http://www2.prnewswire.com/cgi-bin/stories.pl?ACCT=105&STORY=%2Fwww%2Fstory%2F07-27-2004%2F0002218858 |archive-date=8 March 2021 }}</ref><ref>{{cite web |url= http://goliath.ecnext.com/coms2/gi_0199-538206/KOITO-and-DENSO-Develop-World.html |title=HID headlamp system has a newly developed mercury-free discharge bulb |website=Goliath.ecnext.com |date=2004-07-27 |access-date=2010-12-29 |url-status=dead |archive-url= https://web.archive.org/web/20090528162933/http://goliath.ecnext.com/coms2/gi_0199-538206/KOITO-and-DENSO-Develop-World.html |archive-date=28 May 2009}}</ref> but are not electrically or physically compatible with headlamps designed for previous bulb types.

===== Cost =====
HID headlamps are significantly more costly to produce, install, purchase, and repair. The extra cost of the HID lights may exceed the fuel cost savings through their reduced power consumption, though some of this cost disadvantage is offset by the longer lifespan of the HID bulb relative to halogen bulbs.