At a recent visit to PTS Developments in Wokingham,
I mentioned the problem and Pete Sparrow recommended fitting HID gas
discharge (Xenon) lights. These are not to be confused with
regular halogen bulbs with a blue tint; these are the same lights that
are fitted to many top-of-the-range cars and have a light output tilted
towards the blue end of the visible light spectrum.
claimed advantages of HID headlights are higher intensity, longer life,
superior colour, and better directivity.
HID lamps are about 3 times as efficient as halogen lamps. Thus, even
when the efficiency of the DC-DC converter is taken into consideration,
the lower power input can actually result in much brighter headlights
than are possible with halogen bulbs. This reduced power also leads to
cooler operation and less drain on the battery and alternator.
Lifespan - an HID lamp can be expected to last 2,700 hours or more. Essentially, the HID lamp may outlast the car.
Spectral output - the light from the HID lamp is richer in blue (and
more like daylight) than halogen bulbs, thus enhancing reflectivity of
signs and road markings. Furthermore, clothing that contains
white flecks (undissolved washing powder) reflects – as anyone who has
been to a disco with UV lamps can confirm.
Beam pattern - the small arc size of the HID lamp permits the optical
system to be optimised to direct light more effectively to where it is
needed and prevent it from spilling over to where it is not
wanted. Couple this with the complex surface reflectors and you
have an extremely well demarcated beam pattern.
It is necessary to equip the car with a number of electronic
components. The HID bulb itself is similar in basic design to
traditional HID lamps (a common example being the fluorescent tube used
in interior lighting). Two electrodes are sealed in a quartz envelope
along with a mix of solids, liquids, and gasses. When cold, these
materials are in their native state (at room temperature) but are
mostly gases when the lamp is hot. Starting of these lamps may require
up to 20 KV to strike an arc but only 50 to 150 V to maintain it. Lamps
may be designed to operate on either AC or DC current depending on
various factors including the size and shape of the electrodes. A
unique set of ballast operating parameters must be matched to each HID
Of all the problems that had to be addressed for HID headlights to
become practical (aside from the cost), the most significant was the
warm-up time which was solved by programming the controller to deliver
constant power to the lamp rather than the more common nearly constant
current that would be provided by a traditional ballast. With this
twist along with a special lamp design, the lamp comes up to at least
75% of full intensity in under 2 seconds.
As hinted earlier, this is not a cheap solution but is money well
spent; not least because the kit can be removed and fitted to another
car at minimal cost. The standard headlights may be refitted when
it is time to sell the car.
This really is money well spent – especially if you live in a rural
area. My XM is utterly transformed. Driving at night is
much easier. The diffuser was left in situ
and the beam pattern is unchanged. Judging by the failure of
oncoming drivers to flash their lights, they cause minimal annoyance to
other road users.
Clearly, these lights can be fitted to any
car but the law requires any such car to be fitted with either a
headlamp beam adjuster or self-levelling suspension and headlamp