The age old discussion of HID conversions goes on and on, So I thought I would put some facts together for people wishing to carry out this type of conversion.
Please don't flame this thread if you are a HID fan as it is all based on published research etc and opinions are based on facts.
The purpose of this thread is NOT to tell you what you should or shouldn't do, it is a thread that hopefully will give you some facts and opinions that you won't hear at the McDonalds car park meet. It is intended to give you information to help you decide whether it is worth doing and whether it comes with possible consequences.
We have all heard the "It's OK because I have fitted them and nobody has flashed me" and "It has passed an MOT so must be OK" type of arguments, but these are peoples opinions and are heavily biased towards the "I like them so will justify them" catigory.
So, lets dispell some myths first.
HIDs give much better vision.
Correctly designed HID can give better vision, but, many HID conversions only give you better vision in the foreground and can even give you less vision over distance. This plays up to a flaw in human perception. Illuminating the area directly in front of a car does make the driver feel more confident, but this brings problems as it actually reduces your night vision by closing down your iris to compensate for the bright light.
This effect can also be seen in people who swear that driving with foglights on gives them better vision. This is impossible over any usefull distance as the foglight is designed to give a low flat short beam. All it does is increase the illuminated areas around the front of the car, including the verges, in the same way many HID conversions do.
So, in effect, most HID conversions will throw less light into the far field and illuminate the near field more, creating an unjustified level of confidence and may increase the drivers confidence and speed.
HIDs are good for standard headlights.
This is simply not true.
The standard headlight optics have been designed to work with a halogen filament light source which has a standard, replicable focal point. In other words, if you fit a halogen lamp that is to the correct standard then the focal point, or point of light, is the same every time and this is very important for the beam pattern.
HID lamps have a very different focal point. Think of a normal lamp being a golf ball and a HID being a rugby ball. A different size and shape altogether.
You will hear people telling you that the beam pattern is just the same as normal as they have fitted them and have checked them. Not true as this is physically impossible. You may achieve a beam that is close, and it may even pass an MOT, but the beam will be different and can still cause nuisance to oncoming traffic.
HID conversions are legal.
This is another point that can be manipulated by people who want to have them.
The fact is that any HIDs are not legal in the UK by UK law. ONLY filament lamps are allowed by vehicle usage laws.
So, how come new cars have HIDs?
This is because UK law can be superceded by EU law and there is a document that allows HIDs to be used.
So, HIDs are allowed then?
Well, yes and no.
HIDs are only allowed over the UK regulations if they follow the EU law, and that is where the confusion comes in. The EU law states that the headlight unit must be designed for HID, have headlamp cleaning facility AND self levelling. It doesn't provide for aftermarket HID conversions, so the UK DfT interpretation is that HID conversions are only allowed IF they comply with the same specifications as factory fitted units.
I will add to this as myths and other bits crop up, but here are some sites and documents to read.
http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&cad=rja&ved=0CDUQFjAA&url=http%3A%2F%2Fassets.dft.gov.uk%2Fpublications%2Fdft-information-sheets%2Faftermarket-hid-headlamps.pdf&ei=oD7XULy_D-Kv0QXq-oHwDQ&usg=AFQjCNF1WC8dTWAGFHDcd9gBq3Qhidubsg&bvm=bv.1355534169,d.d2k
http://www.danielsternlighting.com/tech/bulbs/Hid/conversions/conversions.html
In the interest of fairness, if you do know of official and legal documents that say you are allowed to fit HIDs then please post them up, as I said this thread is to give relevant info to people wishing to fit them.
Please don't post what you think or what a mate says in a bar etc.
Also, it is worth noting that MOT regulations etc do not over write UK law. A point in the MOT guidelines does not have more weight than the vehicle usage regulations or DfT interpretation of the law. In an ideal world they would say the same though.
I have just noticed an increase in another negative side of HID aftermarket kits.
Most HID kits that people fit will be cheap Chinese kits and these can cause electrical noise due to cheap construction and lack of shielding. Several reports are floating around the internet of failures of critical systems, such as power steering, ABS etc etc.
At first this might seem a bit scaremongering, but, if you are an electronics/electrical based engineer you will know that noise on sensitive electronic systems is the work of the devil and can cause problems from spurious signals to total shutdown.
Most modern vehicles use what is called "Canbus" which is a data network that connects the whole system to the "brains" of the car. If this is disrupted then it is the same as disrupting your nervous system and can have unforseen problems.
Imagine turning your headlights on and all your cars warning lights come on and you lose your power steering. That is what has happened to a Mercedes owner that fitted an HID kit himself. When he took it to the garage they wouldn't touch it with the HID system in place.
http://mbworld.org/forums/c-class-w203/359793-c230-hid-installation-problem-errors-power-steering-failure.html
http://forums.audiworld.com/showthread.php?t=2790793
