4100k they're as close to OEM as possible.
OEM bulbs are Philips 85122 which gradually lose levels of light to around 5000k over time. The ones I've linked are 85122+ which are the same except are meant to stay at 4100k over the years.
Not sure why people choose bulbs with a blue tint and have a lower lumen output.
Now I'm slightly confused... I knew that standard fit was about 4100k but I thought (from my school recollections and current research) that the higher the k number, the brighter the light, up to a certain point where it goes too far. Sure sunlight is about 6500k :-/
k number has NOTHING to do with "brightness" as we use the word.. but is to do with the end of the spectrum the light is equal to. The higher the k number the "bluer" the light will be as it gets closer to the ultraviolet end of the spectrum.
The lower the k number the more "red" the light is.
Human eyes see a fairly narrow spectrum compared to animals, 4100 K is close to the light produced by "incandescent" bulbs.
6500 K has more "blue" and is "supposed" to work better on reflective surfaces like high vis jackets and the paint in white lines. Anything higher and you won't see "darker" objects .. like the pedestrian in a duffel coat.
As alluded to above .. the "brightness" of a light is measured in LUMENs and is a different ball game altogether..
