: Head lights

11-12-07, 06:18 PM
I have a 2007 STS with the 1SG pkg which comes with HID headlights. My question is why are the high beams not HID and if they are why are they the color of the old style headlight?

Northern SRX
11-13-07, 07:10 AM
I am absolutely not an expert on this but I'll chime in with what I've read - right or wrong.

The Cadillac HID set-up is HID low beam with halogen highs. Read on...

Most hi/lo HID set-ups are not separate bulbs but rather shutters in the light assembly that re-aim the light off reflectors to fill in a different spectrum. I have not read about any vehicle that has separate HID bulbs for both high & low beams but, again, I am no expert.

Far more common is the HID low and separate halogen high set-up. This set-up permits instant highbeam usage (for instance, when you think you see a jogger or dear by the road and want a flash of penetrating light just to get a quick sense) as HIDs take a little longer to warm up to full power than halogens do. Halogens are just faster to reach an acceptable illumination level. Keep in mind that HIDs require a ballast to send a blast of ~25000 volts to get started and then a few seconds to reach full illumination power.

Yet another reason I have read for the xenon/halogen lo/hi set-up is redundancy: when the HIDs fail, you at least have some ability to illuminate with the halogens. If you have a HID-only system that serves both as high and low off a single bulb, you have nothing if either the bulb or ballast fails.

Finally, most drivers do not use their high beams for that many hours while driving. It doesn't make a lot of economical sense for manufacturers to install a redundant system to support separate high beam HIDs.

Again, I am no expert so your mileage may vary...

11-13-07, 08:25 AM
Thanks Northern SRX

Your second paragraph makes a lot of sense and that's the setup on the STS. I guess I could swap out the regular halogen bulbs for the super 'white' type to get a closer match to the HID's.