We often get the question: “Doesn’t a higher number mean it’s brighter or better ?”. The short answer – NO. When talking about an HID bulb Kelvin Color temperature, a 4100-4300K HID bulb is the brightest Kelvin Temperature you can get. This is the OEM coloring specification on most vehicles with factory HID headlights for a reason.
Light output is measured in luminosity or lumens. A 4300k HID bulb at 35 watts generally produces 3200-3400 lumens of light. As Kelvin Color Temperature starts to go up (5000k, 6000k and above) luminosity decreases.
A 5000k HID bulb at 35 watts generally produces 3000 lumens and a 6000k HID bulb at 35 watts generally produces in the 2800 lumen range. The lumen output above 6000k starts to dramatically decrease, which is why we never recommend anything above 6000k for an HID bulb. Anything above 6000k should be regarded as cosmetic or show only.
“Why do my friend’s headlights look brighter than mine and he has xxxx-K temperature bulbs???”- The reason higher Kelvin bulbs may appear brighter is that they are actually glaring more off of the road surface. Glare is NOT how light output is measured. It’s annoying, obnoxious and dangerous. Anything above a 6000K color rating is extremely ineffective & can be deemed practically useless. 6000K is generally the highest Kelvin rating you can go without creating too much glare. The higher the Kelvin rating, the lower the lumen output is. (We can’t stress this fact enough…so we noted it twice)
When the Kelvin rating is above 6000K, generally the lumen rating is around 2000 or below. This actually puts the HID output level back in the category of Halogen Output.
What about 3000K HID bulbs? A 3000K HID bulb is designed for foul-weather or fog situations. 3000K produces a yellow light that cuts through rain, snow & fog better than a white light.