I know many of you know what are HID's are but this a simple guide for the people who don't know what they are or afraid to ask or just don't know hoe it really works.
HID stands for High Intensity Discharge. It is a lighting technology that relies on an electrical charge to ignite xenon inert gases that is sealed in a glass jacket(bulb) to filter ultraviolet emissions. The technology of HID automotive lamps is similar to that of common vapor-filled street lamps or other non-halogen lighting found in many buildings today. HID lighting doesn't have a filament but instead creates light by igniting an arc between two electrodes based on the gas discharge principle.
Why use HID?
Darkness on isolated highways is one of the reasons for why HID lighting is becoming popular and necessary.
HID lighting promotes safety by providing a better overall view of the roadway and the ability to see upcoming objects quickly and more clearly. Road signs and objects on the road are easier to see when illuminated by HID headlights when compared to the standard halogen bulb.
Light Output Performance
HID lighting provides about three times or 150% more light output of standard halogen headlights while using less energy
HID lights are designed to last up to 2-3 times longer than standard halogen lamps.
Hid lighting produces 82 lumen's per watt (2970 total lumen's) compared to 18 lumen's per watt for a halogen lighting source (1188 total lumen's). both were done at 4100K* about 5% less with every color jump
The Colors of HID's
OEM(GM,BMW,Dodge,Etc) car manufacturers equip their cars with 4100k to 4300k HID bulbs which produce the most daylight-like light output. Lower temperatures like 3000k will produce deep gold-yellow color, suitable for fog lights. Higher color temperatures will output light with a hint of blue/purple like the 5000k - 6000k bulbs, higher rated bulbs will be bluer and eventually purple in color as you go up the scale. There are also bulbs that come in red and green.
The use of HID's with aftermarket/factory headlights.
This is just a good idea using projectors with HID's provides you with the best output and a cutoff. One thing you might want to take into consideration is that some projectors may have a tint on the glass projector, this will affect your final color. For example BMW uses a Slightly blue tinted projector lens which gives the light an ever so slight blue hint while there using only 4300k.
Now cutoff shields (This is what creates a sharp cutoff when using projectors) may have a tint to them as well. For example Lamborghini uses a pink cutoff shield which if you see an oncoming lamborghini at just the right angle you see pink light.
Here are some light patters With Projector headlights and regular headlights.
Using projectors (Noticed how the left said is Dipped to avoid blinding oncoming drivers)
Using Regular headlights
^^^^ My personal car the best cut-off I could get