Apologies if this is a little off topic but the choice of bulb temperature will determine how "cool"
you look or how bright the road lights up in the day and at night. I also want to bore the pants off pudding
In fact this is a warning for all ... this is a little boring....
HID colour temperatures of 4300k emit the most light (lumens) in the
visible spectrum that you see every day with your own eyes. Hence you can generally see them at night and on darker days like cloudy or rainy days. On sunny days they effectively disappear as all light is mixed and is basically daylight and you only see the bulb really and not the projected light. They are meant to be the equivalent of daylight (full visible spectrum) and hence they output the most lumens.
As you move towards the higher colour temperatures 5500k and 6000k you shift the light
spectrum towards the UV end of the light scale ie more "blue" and you reduce the visible light that you could see. So although they appear bright they are not delivering the most effective amount of visible light (less lumens) and hence are not as good for general driving.
Now the real science begins... Bluer light does however have a higher energy (shorter wavelength) and can penetrate further through mediums like water or air so they appear to see farther. Its a little silly really... they have more energy but less lumens. or light power.
See this
http://www.5gcamaro.com/hid-color-chart/HID's are also more efficient at producing light than halogen and produce more lumens per watt and that's why they are brighter and use less power than halogens.
With age the
efficiency of HID bulbs does decrease by 5% or 10% due to electrode and metal salt degradation (used to provide the actual light as they are ionised in the bulb) and as an example you will see a better light output from a new Xenarc night breaker than the original but they are still operating at the daylight temperature of 4350k so give maximum lumens.
In the end I will always use HID's with a colour temperature of 4300k to maybe 5500k but no more. Beware claims of xx% brighter.... 6000k bulbs are not more powerful in terms of lumens than the standard bulb. They are just shifting it to the blue end of the spectrum.
Are you all asleep now?
Cheers
Rip