BMW BRIGHTENS THE NIGHT WITH XENON HEADLIGHTS
In the early 1970's, the first automobiles appeared with halogen bulbs in their headlights, which gave a far brighter light and a longer beam than the conventional double-filament bulb. Drivers reacted to this new light source with praise. At last, modern cars could have headlights worthy of their performance and that ensured an acceptable level of safety.
Now, BMW has taken the next giant step forward in headlight technology by adopting the xenon light principle -- an even greater advance in automobile lighting technology than the change from the standard to the halogen bulb some years ago. BMW is the first car manufacturer in the world to offer xenon headlights as standard equipment on its 750iL luxury sedan.
"With the new xenon technology, BMW has taken a significant step to 'brightening up' the automotive world,' commented Karl H. Gerlinger, president and CEO of BMW of North America, Inc. "We are very proud of our engineers for this development. But, more importantly, we are excited to offer a car headlight system that provides proven measures of safety to our customers.,
Xenon bulbs and lamps are not new, at least in principle. Evening sporting events have been staged for years under the brightness of large xenon lamps. The problem of compressing those giant units into a form convenient enough for use in an automobile, however, was challenging. In addition, the big lamps have a warm-up time of several minutes, which had to be cut to less than a second in order to be acceptable for road use. BMW has tackled both of these design challenges, and the company is now able to offer xenon headlights that provide four times the light output of the halogen bulbs they replace.
Xenon light has many advantages over conventional lighting methods. The first, obviously, is the availability of more than twice as much light output, for greater night-time safety when visibility in poor. In addition, the xenon lamp lasts up to five times longer than a halogen bulb, and should therefore not need to be replaced for the life of the car. Furthermore, light output from a gas-discharge lamp of this type does not vary regardless of other demands on the car's electrical system, and unlike the halogen bulb is not affected by corroded contacts. This is because the xenon lamp has its own power control system. Despite its high performance the xenon lamp consumes about 40 percent less electric current and dissipates correspondingly less heat.
When the xenon headlight is switched on, the ballast unit delivers a momentary ignition pulse of up to 10,000 volts, followed by an operating current, which is approximately 85 volts. An immensely bright arc is struck between the two electrodes. This takes the place of the usual incandescent filament in a conventional halogen bulb. The light source is projected on the road by the ellipsoidal-principle reflector and lens in a precisely determined pattern.
Xenon headlights are more complex to manufacture than conventional kinds. Among their main components are the electronic ballast unit, the ellipsoidal-principal reflector and the actual xenon bulb. This is not much different in size from the existing halogen bulb, and consists of a quartz glass tube filled with xenon gas and other trace elements, into which electrodes project. The automotive trade code for this bulb is D1, with "D" standing for "discharge" and "1" for the design generation.
The light from a gas-discharge lamp is not only exceptionally bright but also extremely white in color. To prevent dazzling oncoming drivers, the lamp must be positioned very accurately -- something which the projection system used by BMW since 1986 is capable of achieving.
BMW adopted the xenon principle for low-beam headlights, which are more frequently used than high-beam units. BMW's high-beams continue to be HI halogen bulbs which are used for maximum visibility when there is no oncoming traffic.