[Aussie Mike]

One of the advantages of the HID or xenon lights is they draw a lot less power. They are only draw 35 to 55 Watts for a lot more light output. That means less current required than the regular lights and no need for extra relays, heavier wiring etc.

If you are not sure how they work they are actually an arc light rather than a fillament like a regular globe. They have a ballast attached to them that takes a 12VDC input and turns it into a 22KV AC output. This arcs accros a gap inside the globe. The globe is filled with an inert gas that the arc jumps easily through and some metal salts. The arc jumping through the gas starts the reaction. The metal salts are superheated and form a ball of plasma which produces the ultra bright light. This is why when you turn them on they take 10 seconds or so to warm up and they get progressively brighter as more of the metal salts are heated and turn into plasma.

It's the same technology in mercury vapour highbay lights in factorys etc. The Highbay takes a while to warm up because the mercury takes a while to completely turn to plasma. Also anyone who has them will know that when you turn them off and back on again they won't light. The arc doesn't like to jump throught the mercury once it's al vapourized, it just sort of shorts out and flickers purple. You have to let them gool down and let the mercury condense before turning them on again.

It's for this reason you generally won't see HID lights used for seperate high beam lights. They are usually used just for High/low beam lights and the Hi/Lo is done by changing the position of the bulb in the reflector to change the light pattern. The arc stays running the whole time.

Cheers