Originally Posted by Bluefoton
Colour temperature ratings apply mostly to HIDs, not to halogen bulbs. Any filament bulb shifted towards blue is done by filtering out the red (i.e blue coating) - or, to a very limited extend, by increasing the voltage, which drastically reduced their liftetime. H9s are already "whiter" than a lot of OEM halogens...
I think you ment, "increasing the wattage", not voltage.