Owners of 1998 - 2004 Seville models have projector design low beam headlamps. At some point, Cadillac made OEM HID low beam lamps available/optional. My 1998 model did not come equiped with HID low beam lighting. Unfortunately.
I'm in the process of installing a 35W 9006 4,300K HID bulb conversion kit from SharpHID (http://www.sharphid.com/) and I could not be happier with the results. Probably the best $80.00 I have ever spent on aftermarket parts.
I hope the picture says it all. The cut-off line speaks well to the projector lens reflector design. The driving experience is a treat for my tired old eyes.
http://s70.photobucket.com/albums/i101/Jim...eHIDlowbeam.jpg One caveat for folks considering this conversion: I recommend you modify the headlamp control circuit so the low beam (HID) lamps remain ON when the high beam lamps are selected (HID lamps require a few seconds to reach full light output). It's an easy modification with a $0.50 diode.