In the bulb, instead of a filament, there are electrodes that have a bolt of lighting arc across them. They produce a much brighter and whiter light.
The K number is the color temp. It is not the brightness (well not directly, I'll explain). 4000K - 5000K is the brightest. Continuing up the color scale, the light gets bluer then purpler and the lumen output (the actual measurement of light) decreases. In other words, a 10000K HID kit is dimmer than a 4300K HID kit. Our eyes are least sensitive to blue light. Blue light also scatters more easily. In the end, we can see better with a 4300K HID kit for many reasons.
The core components are the bulbs (capsules) and ballasts to ignite them. Each bulb has its own ballast.
HID lighting should be used in HID projectors (some halogen projectors can also support HID fairly well).
HID should not be installed in Halogen reflectors because the resulting beam pattern is almost always wrong. This doesn't stop many people from doing anyway though. What this means is putting a HID kit in place of a halogen bulb like an H4 for example. The beam pattern will be narrow (and often blotchy) and to everyone else it will appear as if your high beams are on. The reason for this is because the HID arc is often not in the same place as the Halogen filament and the halogen reflectors were not designed to handle the light output. We want more light on the road, but not in the eyes of other drivers.
There were a couple OEMs that released HID reflector setups, but that is very rare.
Real HID setups use D1S, or D2S, or D4S capsules and their requisite ballasts and are almost always in projectors. When you see H7, H4, 9005, etc, those are Halogen part numbers, meaning that the kit uses an HID capsule that has had its base changed to a Halogen base so that it fits in place of that model Halogen Bulb.
Here is some more reading: http://www.danielsternlighting.com/t...s/Hid/HID.html http://www.danielsternlighting.com/t...nversions.html http://www.danielsternlighting.com/t...dvantages.html
Check out the Lighting FAQ for more: http://www.ls1tech.com/forums/appear...hting-faq.html
Also, technically, installing HID in a car that didn't come from the factory with it (or it was an option) is illegal. Its a technicality, but if installed properly with projectors, its doubtful anyone will notice or bother you. I and others have done some conversions with projectors. Check out the Lighting FAQ.
Check out www.hidplanet.com/forums/
for a wealth of information. They are kinda the LS1Tech of HID. I'm on there too with the same screen name.
As for major companies, Phillips & Osram (Sylvania) are the two biggest manufactures of real HID products (D1S, D2S, D4S and their requisite ballasts). There are plenty of third-parties, cheap knock-offs, and conversion kits all over the web though. Since I have a H9 conversion kit in my projectors, they technically fall into this second category, although I am using projectors.