Alright, here lately we've had alot of new members show up and ask very basic, already covered info. So i took it upon my self to cover the bases so to speak so that you get a general idea of what all is involved with HID.

Class is in session...shall we start?

Bulbs
Ok, first off, lets start with the bulbs. The common mistake some people here is that all these high kelvin rated bulbs are the shizzle. Well, they couldn't be more wrong. The higher you go in kelvin, the less light and lumens you'll have. Pratically anything over 6k is really a waste if your at all concerned with your safety and brightness of lighting. So what is the best bulb out there then you ask? 4100-4300k. It has the most lumens out of all the HID bulbs produced. Thats why car manifacturers still use them today. Below is a graph showing you the variances of the light spectrum. As you can see, 4100k would be right where the "sweet spot" is on that chart. It produces near to the suns same kelvin thus giving you daylight-like output. Think of it like this, high kelvin bulbs would be like being out in the sun with sunglasses on vs a 4100k being in the sun w/o glasses on.

Also here is another good thing to know taken from the FAQ:
Yellow:
1500 k Candlelight
2700-2900 k Yellow painted fog halogen bulbs
-------------------------------
Yellowish white:
3200 k Sunrise/sunset
3200 k Premium H7 non painted halogen bulb
3400 k 1 hour from dusk/dawn
-------------------------------
White:
4100 k Philips/Osram OEM HID D2S
5500 k Bright sunny daylight around noon
----------------
Blueish white
5500-5600 k Electronic photo flash
6000 k Philips Ultinon HID D2S
6500-7500 k Overcast sky
-----------------
Blue:
9000-12000 k Blue sky
-----------------
Purple:
28000 Northern sky
12000-30000 k Ultra Violet light (black light)

Some important terms to know:
Watt- Measure of electrical power (w)
Volt- Measure of electrical charge (v)
Kelvin- Measure of color temperature (K)
Lumen- Measure of light brightness (lu)
Capsule- tecnically correct term for a HID "bulb".
Candela- Measure of light intensity (cd)
Ampere- Measure of electrical current
Cut-off- A distinctive line of light produced by the shield in a headlight that blocks light above a certain height in order to prevent blinding of other motorists.
Beam Pattern- The pattern of light that is projected onto the ground which includes angle of lateral dispersion, width and depth of illumination.
Capsule- Another term for an HID bulb. Some refer to HID bulbs as gas discharge capsules.
Optics- The lighting control assembly structured around the bulb, which effects the dispersion of light and it's characteristics to a great degree.
HID (High Intensity Discharge)= Gas Discharge
Halogen= Incandescence



So now that you know about kelvin and some aspects of the bulbs, you might be wondering why you hear the terms D2R or D2S. Well, to put it very simply to you, D2R is a HID bulb that was designed for HID reflector housings. It has a different base than a D2S and also has a painted portion on the bulb itself. Why is it painted you ask? The paint is there to block certain areas of the bulb that would cause excessive glare in the housing. Does the paint affect bulb performance? Yes. A 4100k D2R has slightly less lumen than a 4100k D2S. Can a D2R be converted to a D2S? Yes. You would have to make a notch in the base of the bulb to match that of a D2S. you would also need to delicatly remove the painted portion of the bulb so that it would be completely visible just like a D2S. So enough about a D2R ehh, lets talk about the D2S for a sec. The D2S was designed soley for a HID projector applications. They are completely clear and give out the most efficiency of the two. Thats pratically all there is in difference between those two bulbs Below are some pics of both.
D2R
D2S
Lets move on shall we...