blue is actually the most intense in the colours of a light spectrum. thats why you see blue on police cars ect. the intensity carries the furthest.(even through fog, snow and rain) light is measured in kv (kelvin units) the higher the number, the more blue they will be. for eg. a 6000 k headlight is not as blue as a 8000k . factory HID headlights that you will find on a new bmw or benz are around 5000k. on the same note, switching over to a HID setup is literally a night and day difference when it comes to headlights. phun intended. LUMENS makes an awsome conversion kit. hope this helps
Food for thought........
I upgraded the factory HIDs on my DD from 4300K bulbs to 6000K. In doing my research, several sources said not to exceed 6000k because, although the 8000K light is brighter, it has a shorter effective distance. Basically, other people will see you better, but you won't see out better. I will admit that even with the increase I did, I feel more compelled to use my fogs more on dark roads. I just don't feel like I can see as well as I did before the "upgrade". I really like how they look though, and I have my fog/driving lights (which are just as bright as headlights) to make up the difference.
I do know this: Different light sources produce different wavelengths of light, and lower frequency waves travel further than high frequency waves. My guess is that the higher temp of the lights produces higher frequency (visibly brighter) wavelengths, but their effective area is decreased. IMO, the best middle ground is 5000K-6000K.