Originally Posted by calvin2376

Brightness is measured in lumen output. Color is measured in temperature. The higher the color temperature, the lower the brightness in lumen output. So in terms of brightness, 3000K (yellow, like fogs) will be brighter than 6000K (bluish white) or 8000K (purple).

The stock HID bulbs I believe are 4100K (either than or 4300K). If you get a higher color temperature, your brightness will be lower. However, if you've had the same stock HID bulbs for a long time they may have faded a bit, both in terms of color and brightness, so replacing old 4100K bulbs with something like 5000K bulbs can actually increase brightness, only because the old ones are faded. Some will argue that higher color temperatures like 8000K are brighter than stock, but this is just the eye's perception when looking straight on - in terms of true brightness, lumen output, and functional road illumination, lower color temps are better.

If you have stock HIDs you won't need ballasts, you can just buy replacement D4S bulbs and swap them out. If you have stock halogens (non -HIDs) you'll need an HID kit with bulbs and ballasts.