A must read is Dan Stern's site on lighting:
http://lighting.mbz.org

Specifically his articles on "blue bulbs":
http://lighting.mbz.org/tech/info/bulbs/blue/

and the myth of PIAA "SuperWhites":
http://lighting.mbz.org/tech/info/bulbs/superwhites/

Please also read his whitepaper to the NHTSA, "Where does the glare come from".

The PDF is here: http://dms3000.dot.gov/docimages/pdf82/176157_web.pdf

Pay close attention to pages 43-45 of 66 pages total. In short, HID retrofits into a headlamp designed for a tungsten/halogen lamp might yield *brighter* light, but too much glare. HID's are an "arc" and as such, need headlamp reflectors/optics optimized for an "arc".

:-) neil
1988 360TE AMG
1993 500E