# Those really bright headlights **URL:** \ **Category:** Factual Questions\ **Created:** [September 28, 2004, 6:29pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533 "2004-09-28T18:29:18Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [September 28, 2004, 6:29pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/1 "2004-09-28T18:29:18Z")
Ever since the early 1990s, I’ve noticed that there are some cars that have really bright headlights. When they shine in my direction I’m temporarily blinded. It’s similar to having high beams flashed at you, but the quality of the light is noticeably different – something like a halogen bulb. What’s up with these lights and why do people have them? And why aren’t they banned as a hazard? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [September 28, 2004, 6:34pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/2 "2004-09-28T18:34:52Z")
They are called [HID lamps](http://www.onemotoring.com.sg/publish/onemotoring/en/topwebwide/faqs/vehicle_modification.html). > [@](#): > > Unlike normal halogen headlamp systems, HID headlamps do not use a filament. Instead, they contain an inert gas (Xenon), which emits light when it comes in contact with a high-voltage electrical arc. > > HID lamps produce up to twice as much light as halogen lamps, with a bluish-white cast and minimal fading at the periphery of the beams. However, the brightness perceived by an individual depends on the distance from the light source, beam direction, relative brightness of the surrounding environment, and other factors. > > Nevertheless, HID lamps have been proven to improve visibility. A motorist using an HID lamp system is able to see about 100 metres to the front of the vehicle, compared to about 58 metres with standard halogen lighting. ---
**Author:** ![jayjay](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jayjay/32/6765_2.png) [@jayjay](https://boards.straightdope.com/u/jayjay)\ **Post date:** [September 28, 2004, 6:41pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/3 "2004-09-28T18:41:46Z")
> [@Q.E.D.](#): > > They are called [HID lamps](http://www.onemotoring.com.sg/publish/onemotoring/en/topwebwide/faqs/vehicle_modification.html). As opposed to, say, the motorist in the opposite lane who, when confronted by these evil monsters of technology, can’t see ANYTHING until his rods and cones recover. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [September 28, 2004, 6:54pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/4 "2004-09-28T18:54:47Z")
I’ve got them, and I’m undoubtedly driving around annoying people with my purple headlights. I didn’t really want the feature - they just happened to be on the car I purchased off the lot. I’m glad I got them. Not so much for seeing directly ahead of you, but for peripheral vision. When I first got the car, I was quite amazed at how well those things lit up the side of the street. Particularly good for suburban residential areas at night. There were similar complaints when most cars went to halogen bulbs, if you remember. We got used to them. Auto leveling systems on later cars with HID headlights help. They supposedly last a long time, too, which is good, because they cost an arm and a leg to replace. ---
**Author:** ![Phlosphr](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@Phlosphr](https://boards.straightdope.com/u/Phlosphr)\ **Post date:** [September 28, 2004, 7:04pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/5 "2004-09-28T19:04:54Z")
I do not know if they are the same thing, but my wifes mercedes has them, and yes they are very annoying. I remember lifting the hood up and seeing the sign on the lamps saying…that they should only be replaced by factory trained technicians…maybe that is because of the gas inside them? ---
**Author:** ![Berkut](https://avatars.discourse-cdn.com/v4/letter/b/a88e57/32.png) [@Berkut](https://boards.straightdope.com/u/Berkut)\ **Post date:** [September 28, 2004, 7:20pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/6 "2004-09-28T19:20:41Z")
More likely due to the risk of electrical shock. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [September 28, 2004, 7:23pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/7 "2004-09-28T19:23:08Z")
> [@phlosphr](#): > > …that they should only be replaced by factory trained technicians… There probably several reasons. The first is the high voltages involved with HID systems. [This site](http://members.misty.com/don/d2.html) suggests a 20 kilovolt hot starting voltage. Dangerous to be sure. Another reason is the high heat associated with arc lamps. I can’t find a site at the moment with reliable data but suffice to say at least a few hundred degrees. Along with the heat is the pressure. The above linked site gives 30 atmospheres, about 450 psi. You don’t want to have a drop of sweat fall on the hot bulb at these pressures. Greases, oils, dirt and other contaminants alter the transparency of the bulb quartz. Often, this results in much higher heat on the quartz, resulting in failure. Never handle HID (or halogen) bulbs with bare fingers. There is some amount of mercury in the bulb’s chemistry. Mercury exposure can’t be good. ---
**Author:** ![testride](https://avatars.discourse-cdn.com/v4/letter/t/a6a055/32.png) [@testride](https://boards.straightdope.com/u/testride)\ **Post date:** [September 28, 2004, 10:55pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/8 "2004-09-28T22:55:30Z")
Only a relatively small number of cars on the road have HID headlamps. A much larger problem is vehicles with ordinary headlights that aren’t properly aimed. This is a special problem for SUVs because their lights are mounted higher than on the average sedan, sometimes by a couple feet; if you’re sitting in an econobox you’re looking up at the oncoming headlights. Even the distinctive blue color of the HID lamps isn’t a sure tip-off; you can buy standard bulbs tinted blue as some kind of status symbol. But a properly aimed bright lamp won’t bother you as much as a standard bulb aimed straight into your brain. ---
**Author:** ![antechinus](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@antechinus](https://boards.straightdope.com/u/antechinus)\ **Post date:** [September 28, 2004, 11:08pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/9 "2004-09-28T23:08:06Z")
It is a legal requirement to have [an automatic leveling mechanism](http://www.designnews.com/article/CA198794.html) fitted to the HID to reduce the risk of dazzling oncoming drivers. I suspect this is a major reason that only professionals are allowed to change bulb - to prevent a DIY mucking up the mechanism. ---
**Author:** ![antechinus](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@antechinus](https://boards.straightdope.com/u/antechinus)\ **Post date:** [September 28, 2004, 11:28pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/10 "2004-09-28T23:28:47Z")
> [@antechinus](#): > > It is a legal requirement to have [an automatic leveling mechanism](http://www.designnews.com/article/CA198794.html) fitted to the HID to reduce the risk of dazzling oncoming drivers. > > I suspect this is a major reason that only professionals are allowed to change bulb - to prevent a DIY mucking up the mechanism. Also a washing system must be installed to reduce scatter off the light cover. And not ‘legal requirement’ but a mandatory requirement for new cars. ---
**Author:** ![Berkut](https://avatars.discourse-cdn.com/v4/letter/b/a88e57/32.png) [@Berkut](https://boards.straightdope.com/u/Berkut)\ **Post date:** [September 28, 2004, 11:59pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/11 "2004-09-28T23:59:20Z")
BTW, the auto leveling system is not required in the US. ---
**Author:** ![umop\_ap\_sdn](https://avatars.discourse-cdn.com/v4/letter/u/dbc845/32.png) [@umop\_ap\_sdn](https://boards.straightdope.com/u/umop_ap_sdn)\ **Post date:** [September 29, 2004, 1:41am UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/12 "2004-09-29T01:41:27Z")
They appear to use a similar composition to those bright white metal halide lamps used in stadiums and parking lots. Not surprising somebody thought to R&D them for car headlights, but one would expect they’d need a pretty big ballast to run off 12V. ---
**Author:** ![beltbuckle](https://avatars.discourse-cdn.com/v4/letter/b/3da27b/32.png) [@beltbuckle](https://boards.straightdope.com/u/beltbuckle)\ **Post date:** [September 29, 2004, 2:19am UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/13 "2004-09-29T02:19:39Z")
While we are on the topic… Since HID lights have no filament, but instead use an arc, what is their expected life time? I would think it would be longer. Also, I am wondering how much current they draw compared to a common auto bulb. ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [September 29, 2004, 3:05am UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/14 "2004-09-29T03:05:21Z")
Now you can get an HID lamp as a [flashlight](http://ledmuseum.home.att.net/lc100.htm). ---
**Author:** ![flight](https://avatars.discourse-cdn.com/v4/letter/f/bbce88/32.png) [@flight](https://boards.straightdope.com/u/flight)\ **Post date:** [September 29, 2004, 12:10pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/15 "2004-09-29T12:10:34Z")
They are great for driving at night. I was amazed the first time I turned on the brights on a back country road. It was like daylight. ---
**Author:** ![hammos1](https://avatars.discourse-cdn.com/v4/letter/h/ba8739/32.png) [@hammos1](https://boards.straightdope.com/u/hammos1)\ **Post date:** [September 29, 2004, 12:54pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/16 "2004-09-29T12:54:42Z")
They are also an increasingly popular target item for [thieves](http://abclocal.go.com/wabc/news/7onyourside/wabc_7side_091503headlights.html) ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 30, 2004, 1:58am UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/17 "2004-09-30T01:58:10Z")
> [@Phlosphr](#): > > I do not know if they are the same thing, but my wifes mercedes has them, and yes they are very annoying. I remember lifting the hood up and seeing the sign on the lamps saying…that they should only be replaced by factory trained technicians…maybe that is because of the gas inside them? At least on the cars I teach on the reason for the factory trained technician note is for two reasons 1. The voltage involved is very high. Up to 25,000 volts to start, and then it tapers down to only about 85 volts when the lamp is fully warm. which brings us to the second reason 2. Heat. The bulbs run at about 750-800 degrees F. The ballest runs at about 200 degrees F. Either would give a severe burn. Enough that a legal disclaimer is not a bad idea. ---
**Author:** ![Anachronism](https://avatars.discourse-cdn.com/v4/letter/a/e56c9b/32.png) [@Anachronism](https://boards.straightdope.com/u/Anachronism)\ **Post date:** [September 30, 2004, 12:06pm UTC](https://boards.straightdope.com/t/those-really-bright-headlights/266533/18 "2004-09-30T12:06:00Z")
I remember reading one article (sorry no cite), that there where also a large number of complaints about headlights being to bright when auto electrical systems first went from 6 volts to 12 volts. However, the biggest problem with HID lights are the aftermarket kits installed by people who don’t know what they are doing. The white light of HIDs is considered cool so many of the ‘ricers’ put them in their cars. If you put an HID bulb in a housing not designed for it it is probably going to scatter a lot of light and blind other drivers. Other drivers get blinded by these poorly installed aftermarket kits then assume all HIDs are bad.