Mozzie,
Xenon headlights are also known as HID's (High Intensity Discharge) lights. They use a xenon gas filled bulb and a projector to emit a light beam as opposed to a standard halogen light which essentially bounces light off a curved mirrored surface.
Xenon h/lights are very easily identified by slightly different hues of blue, purple, white etc when viewed from different angles. You may recall seeing an HID equipped vehicle going over a speed bump at night time, it's quite noticeable when doing so.
Xenon h/lights are completely different from halogen lights when viewed from a distance. They emit a much whiter (usually) and far brighter light beam.
Asides from the above, HID h/lights have several other advantages over halogens.

You might find this rather informative as it details exactly what you are asking. It's bit of read but well worth being informed if you so desire: intellexual net · m k i v

Also check out this thread by Twins Poppa: Any one with experience with this HID Kit ... (Check out Post #44).

GL

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