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.

Color temperature is what usually catches your eye when you spot an HID equipped car on the road. The Kelvin bulbs will appear "brighter"
to oncoming traffic, but in reality they output less visible light onto the road.

What is HID Lumen?
Lumen is a unit of measuring the light output, brightness, of a source. Traditional low-beam halogen headlight produces 1000 – 1200 lumens, while HID outfitted headlight outputs around 3200 lumens.
4100k - 4300k is the ideal HID color temperature to produce the maximum amount of light, lumens, hence the reason while all OEM manufacturers equip their vehicles with these types of bulbs.