"Color Temperature is a measurement in Degrees Kelvin that indicates the hue of a light source, in this case the HID bulb. People not familiar with lighting may believe that the higher the Kelvin the brighter the light will be, this is false. OEM car manufacturers equip their cars with 4100k to 4300k HID bulbs which produce the most daylight-like light output. Lower temperature 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."