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.

The following is the legal rationale:
The Road Vehicle Lighting Regulations 1989 regulate the situation in the UK.
Under these Regulations, HID/Gas Discharge/Xenon headlamps are not
mentioned and therefore they are not permitted according to the strict letter of
the law.

However new vehicles have HID headlamps. This is because they comply with
European type approval regulations. The UK cannot refuse to register a vehicle
with a European type approval. These approvals relate to ECE Regulation 98
(for the HID headlamps which are tested on a rig in a laboratory) and ECE
Regulation 48 (lighting installation on the vehicle).

For the aftermarket, a used vehicle cannot obtain type approval because this
only applies to new vehicles. However DfT does not think it reasonable simply
to ban HID in the aftermarket. Instead the Department makes analogies with
new vehicles. It seems reasonable to require HID in the aftermarket to meet the
same safety standards as those for new vehicles. The same level of safety
should apply.

Therefore a HID headlamp unit sold in the aftermarket should:
1. be type approved to ECE Regulation 98 as a component;
2. when fitted to the vehicle should enable ECE Regulation 48 to be
complied with (although no government inspection will take place); and
3. 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 selflevelling
(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 headlamp unit for
use with HID bulbs. The entire headlamp unit must be replaced with one
designed and approved for use with HID bulbs and it must be installed in
accordance with the rules stated above.