Aftermarket HID conversion kits
A number of modern vehicles are fitted with much brighter headlamps as either standard or as an OEM upgrade option, these lamp are HID (https://en.wikipedia.org/wiki/High-intensity_discharge_lamp) High-Intensity Discharge.
As a quick overview these lamps do not have a filament but a chamber filled with a xenon gas, when an electrical current is passed through two electrodes an electric arc ignites the gas thus producing a very bright arc. Manufacturers then spend a lot of time and money developing a lamp surrounds, reflector configurations and lenses to direct the light produced to the correct position ahead of the driver and to make sure drivers of oncoming traffic are not blinded with bright light.
Typical Dip beam spread is similar to the picture here remembering this is for a right-hand drive car. As you can see the beam lights the Nearside of the carriage way in front of the driver and a little to their right hand, as shown the majority of the light beam stays on the left of the centreline of the carriageway so as not to dazzle oncoming traffic. This is achieved by the shape of the reflector and headlamp lens and the position of the filament within the lamp unit.
With a HID lamp, as they do not have any filament, the light source is much harder to control, and if you look closely at OEM light units you will see the inetivily all has a big optical lens within the unit. As shown to the left. This effectively controls the light out put simarily to that of a conventional fliament type bulb.
The UK Law regarding HID Lamps and convesion kits.
Here are two quotes (A & B) from a document issued by the Department for transport (Uk Government) regarding the fitting of aftermarket HID conversion kits to vehicles used on the roads of the United Kingdom, click on the like to read the full document. (http://webarchive.nationalarchives.gov.uk/20120606172804/http:/assets.dft.gov.uk/publications/dft-information-sheets/aftermarket-hid-headlamps.pdf)
A. In the Department for Transport's (DfT) view it is not legal to sell or use after market HID lighting kits, for converting conventional Halogen headlamps to HID Xenon. If a customer wants to convert his vehicle to Xenon HID he must purchase completely new Xenon HID headlamps. The reason for this is that the existing lens and reflector are designed around a Halogen filament bulb, working to very precise tolerances. If one places a HID "burner" (bulb) in the headlamp, the beam pattern will not be correct, there will be glare in some places and not enough light in other places within the beam pattern.
B. Therefore a HID headlamp unit sold in the aftermarket should: i. be type approved to ECE Regulation 98 as a component; ii. when fitted to the vehicle should enable ECE Regulation 48 to be complied with (although no government inspection will take place); and comply with RVLR as far as "use" is concerned.
In practice this means: 1. The headlamp unit (outer lens, reflector, bulb) shall be type approved to ECE 98 and be "e-marked" to demonstrate this. That can only be done by the headlamp supplier - Hella, Valeo etc. - who must test the headlamp in an independent laboratory.
2. Once fitted to the vehicle it must have headlamp cleaning and self-levelling (which can be for the headlamp or can be in the vehicle suspension - some expensive estate cars have "self-levelling suspension" and that is adequate). Also the dipped beam must stay on with the main beam.
3. The headlamp must be maintained in good working order, kept clean, and aligned/adjusted correctly in the same way as any other headlamp.
Under the Road Traffic Act 1988 it is an offence to supply, fit or use vehicle parts which are not legal. In summary: it is not permitted to convert an existing halogen.
So as a Summary.
The Fitting of an aftermarket or a non OEM HID lighting kit to any vehicle that will be used on the roads of the United Kingdom certain criteria must be met and failure to do so MAY result in either a legal challenge by the Police, Department of Transport Officers or and MOT test failure. It should also be realised that if an accident has been caused by you headlights not being correctly aligned then there is a possibility of your insurance being rescinded due to unauthorised modification to your vehicle.
• The lighting pattern produced must be the same as the original light fitment. • The Headlamps must be fitted with an independent or vehicle based self-levelling system. • The headlamps must have a system to keep the lenses clean.
The choice is yours.
Note:-To prove the above there are some could videos on Youtube expaining the problems.