I'm no expert, but I just Googled HID lights. Here's a quote:
"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 bulb.
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."
"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."
Just type "HID lights for car" into whatever search engine you use, and you will get more information than you could ever need.