[xenon]

^^ yes, the same bulb operates at two levels of brightness, variable output from the LKM.

[beemerbird]

Ian, have you ever thought of going on Mastermind at all?

[xenon]

Specialist subject: the design and workings of the BMW headlamp, 1999 to 2008..

[beemerbird]

Originally Posted by xenon

Specialist subject: the design and workings of the BMW headlamp, 1999 to 2008..

[dxb335d]

Originally Posted by fyonn

this is due to one of the differences between xenon and halogen lights. Halogens light up instantly, but xenons don't, they take a few seconds to warm up before hitting full brightness. This means that they are no good for use as a flasher as they're not quick enough. it would also shorten the bulb life.

As xenon said, on cars equipped with xenon lights, they're actually bi-xenon. IE the dipped lights are the same bulb as the main beam lights, but for a moveable shutter. the inner lights are mostly to allow you to "flash" another driver. On my e90, when I activate main beam, the shutter lifts on the outer lights and it also lights up the inner halogen "flasher" lights. not sure how much they really contribute though.

another bit of trivia, car "xenon" lights are not xenon lights at all, but a form of metal halide lighting. real "xenon" lightbulbs are about 2-3ft across and are typically used to light up the star on stage at a concert, or to show you an imax film.

the name xenon in car lights comes from the fact that xenon gas is used instead of air inside the bulb, but many halogen lights also use xenon gas in this way.

also, I beleive the first production car to feature xenon headlights was the BMW Z1.



dave

Wow, i always wondering why some people never noticed me flashing.

[xenon]

Originally Posted by fyonn

this is due to one of the differences between xenon and halogen lights. Halogens light up instantly, but xenons don't, they take a few seconds to warm up before hitting full brightness. This means that they are no good for use as a flasher as they're not quick enough. it would also shorten the bulb life.

This was the case, but no longer. In fact, it's not shortening the bulb-life that was the problem, rapid-switching shortens the life of the ballast and the ignitor (which are now combined). Nevertheless, cars generally had a xenon source for low-beam with, on bi-xenon cars, a mechanical shutter to give high-beam. This generally meant you also had a halogen main beam light to flash with and to give some assistance to the xenon source on high-beam, as Dave said. On bi-xenon cars, the halogen reflector on the conventional light had a different reflector shape to spread the light closer to the car as the xenon took care of the distance.

Anyway, with more modern combined ignitors and ballasts it is possible to flash with the xenon source only, which is what the e92 does. If you have no lights on at all and you flash the lights, it is the xenon D1S bulb that flashes.

[creepy coupe]

Originally Posted by fyonn

another bit of trivia, car "xenon" lights are not xenon lights at all, but a form of metal halide lighting. real "xenon" lightbulbs are about 2-3ft across and are typically used to light up the star on stage at a concert, or to show you an imax film.

Or arch lights, which refers to the jump the electrical current has to make across the electrodes, which if I'm not mistaken is what a Xenon does.

[xenon]

Not quite, Del.

An arc light uses an electrical arc (like arc welding) to provide the light; Gas Discharge creates a plasma in the gas when excited by the high-tension - this gives off the light.

[creepy coupe]

Originally Posted by xenon

Not quite, Del.

An arc light uses an electrical arc (like arc welding) to provide the light; Gas Discharge creates a plasma in the gas when excited by the high-tension - this gives off the light.

So Ian, does the arc not have a protective surround of gas to help control the burn and if not can I assume the electrode burns away in time?


EDIT.. It's ok found this

An arc lamp or arc light is the general term for a class of lamps that produce light by an electric arc (also called a voltaic arc). The lamp consists of two electrodes typically made of tungsten which are separated by a gas. The type of lamp is often named by the gas contained in the bulb; including neon, argon, xenon, krypton, sodium, metal halide, and mercury.

[xenon]

Yes and yes. The noble gas is very often xenon too, or a mixture of that and other gases. In actual fact, it's semantics really - a gas discharge and an arc light both create light by passing current through a high-pressure gas creating a plasma or an arc.

The electrodes can and do erode - this is what causes a bulb to fail, but this is reduced by having a very stable current supply once the lamp has been ignited. Erosion occurs mostly during ignition which is why it was said earlier that flashing them is not a good idea but in a vehicle application it tended to be the electronics that failed first.

[KD]

Its like being back at school.

And I still don't understand a word

[squeezebm]

Originally Posted by KD

Its like being back at school.

And I still don't understand a word