Xenons and Bi-Xenons - FYI

jayok

Further to a previous post on the subject that I am still getting grief over via PM. I would like to clarify technically the type of headlight bulbs (extract from http://www.acuramdx.org/forums/showthread/t-13240.html)

Xenon headlamps:

They use a type of HID bulb. Most manufacturers with xenons only for the low-beam headlamp lighting will refer to them as xenons. The high-beam is produced by a conventional halogen builb.

I think at one point some manufacturers fooled with having two pairs of xenon bulbs, one for low-beams, the other for high beams. I'm not sure if any such passenger vehicles are available now, as the cost of such systems is quite high and the housings are quite large. Also, since high-beams are often switched on and off quickly, the xenons are less suitable because they need more time than halogens to "warm up" (and frequent on-off will hurt the expensive bulbs). Even worse, a xenon that starts up will not have the same color temperature as it will when it's warmed up. Thus someone switching on a pair of xenons for high beams would get a color shift effect since it won't quite match what they were seeing with the low-beam xenons illuminating the road ahead.

Some manufacturers mount low-beam xenons in a reflector housing. Other manufacturers mount their xenons in projectors, which, all other things being equal, provides a more precise, focused beam with less glare.

Bi-xenons

These use a single pair of xenon lamps to provide both low and high beams. Most implementations I know of are projectors, as theywork best for the bi-xenon effect.

With bi-xenons projectors, a moveable shutter controls the distribution of the beam. When the high beams are activated, the shutter moves up, allowing more light to pass through, and light to distribute up high -- thus, high beams.

The bi-xenons are thus much more effective than having separate xenon bulbs for high beams. They require no warm-up time. E.g. if you're driving with your bi-xenon headlamps on low beam, the bulbs are already powered up. Turning on high beams simply flicks the shutter open (very quickly). Whereas turning a xenon bulb on or off is problematic because the bulb needs time to warm up, and it also hurts the bulb's life. Also, when the switch is made from low to high or vice versa, there is no color shift because the same bulbs with the same color temperature are being used for illumination.

Most xenons continue to use a conventional halogen bulb for flashing.

In summary, xenons are good, bi-xenons are better. The best xenons have auto-leveling systems that adjust the angle of the bulbs to prevent glare, and also have powerful headlamp washers to keep the lenses clean. Dirt, mud, etc. on a lens will cause more glare on a xenon bulb than a halogen bulb, so it's important for them to keep clean.