Posted by murmini Wed, 13 Dec 2006 16:25:22 GMT
The MINI Xenon headlamp system is one of those options that you really need to experience to appreciate.
Stunning blue-white light that truly illuminates with a surreal quality, this technology can offer up to a 70% increase in light output compared with the standard halogen headlamp. Unlike halogen lamps, Xenon have no coil or filament and subsequently they are a much more robust unit offering up to 3,000 hours of life per bulb. The lack of filament makes them much more resilient to vibration and shock and the efficiency of the design draws considerably less current for a much greater light output. The blue effect comes from the fact that they operate at a much higher 'color temperature' at the bluer or cooler end of the visible spectrum. This high end of the color spectrum with very short wavelength light is where the effectiveness of these lights comes from. Many after-market 'blue-coloured' lights do nothing but add a filter or coloration to the light while doing very little to the actual light energy within this spectral range.
So instead of using a filament, that heats up and glows when voltage is applied, as is the case with incandescent lamps, the Xenon light source creates light from an electrical discharge between two electrodes in a microenvironment of xenon gas. This is all sealed into a small quartz capsule. The arc tube is encased in a special glass jacket that filters the light to eliminate harmful ultraviolet rays. The light is emitted by an electrically energized gas plasma discharge that is sustained between the two electrodes. This type of light is often referred to as an HID or High-Intensity Discharge light as well as by Bi-Xenon, or Xenon, named after the gas that sustains the arcing electrodes.
These lights are capable of producing 2500 - 3000 lumens of light, for the meagre consumption of about 40 watts or power. While halogen lights only produce around 700 lumens for a similar power consumption. The arc within the tube has a special glass casing to prevent the ultraviolet light form escaping as it would cause havoc to the hardened polycarbonate lenses found in many modern automotive light units. The other feature of these lamp units is that the light source from the arc has to be gathered and focussed so as not to produce a dangerous glare. This is the reason why so many after-market Xenon bulbs are ineffective and frequently illegal. The Motor Vehicle Lighting Council has produced a nice little flier on Xenon lights
Below is the Xenon D2/S used in the MINI, the hig voltage warning on the side of the firing unit and the optical lens on the front of the light.
Xenon headlamp bulbs do not run on the standard 12 volt DC circuit like the standard halogen bulbs. They require a ballast for normal operation as well as a very high voltage ignitor. The ignitor is capable of delivering 25,000 volts as it 'fires' the arc. A special interlocking safety switch has been designed into the ballast/ignitor so that it is impossible to connect power to the ballast with a bulb removed and subsequently the bulb contacts exposed.
When the headlamps are switched on, the ignitor delivers high frequency pulsed current at about 25 thousand volts to establish the arc between the electrodes within the bulb for a very brief period of time. Once the arc is 'fired' and starts to vaporize the metallic salts within the arc chamber, the power transitions from startup operation to a stable arc-maintenance. This is achieved by the ballast delivering 85 volts to the arcing electrodes. Some of the newer mercury-free lamps are now using 42 volt ballasts and consume even less power.
All Xenon lights require additional systems to keep them safe and free of glare. One is the on-board light washers - on the MINI these are two small jets that come out of the chrome bezel that surrounds the headlamps and squirt water over the polycarbonate headlamp front cover. There is also a system of sensors, one on the front suspension left control arm and one on the rear suspension left control arm. These monitor the 'attitude' of the car and as the car points up, due say to an extra load in the rear or some 'spirited' acceleration, in fact anything that causes the vehicle to change its 'attitude' or inclination, the the lights are 'ratcheted' down to compensate. When you heave on the breaks, or something causes the front to dip, then the lights come up. These sensors are controlled by the general Body Module, which I will get around to describing in more detail at some point.
So all in all the Xenons are a great option and provide the added security for driving at night and in inclement weather. They are also have a very sweet lens arrangement as seen above and look incredible when they fire and then float up and down.