by Jim Kerr
Headlamps have come a long way from the simple incandescent bulb that provides little more light than a candle does in a dark cellar. In the recent past, vehicles used sealed beams. Halogen headlamps have now become the standard for most vehicles, providing much brighter and farther ranging illumination than the older style sealed beams.
Recently, many luxury vehicles and a few economy vehicles have began to use Xenon headlamps that provides up to 60% more light than even halogen lights. Now Mercedes-Benz has taken the next step in improved lighting systems.
Working with Hella, a world-renowned lighting manufacturer, Mercedes-Benz has made a new Bi-Xenon headlamp system available on their E-Class 4Matic wagon models. The system provides up to 90% better illumination than even regular Xenon headlamps.
Bi means two, and Bi-Xenon refers to two lights in one unit. Both low beam and high beam are Xenon lights. There is really only one filament inside the bulb projector unit but it is used for both high and low beams. To switch from one to the other, a mechanical shutter is moved electrically to its raised position to focus the light through the lens for low beam and the shutter is lowered to focus the light for high beam. Rather than move the shutter when the driver wants to “flash the high beams to pass” as they do in many European countries, there is an additional bulb that provides the brief flash of light.
Part of the better illumination provided by the Bi-Xenon system is because both low and high beam use the Xenon bulb. Most Xenon systems have only low beam and use a conventional halogen bulb for high beam. Xenon bulbs provide twice as much illumination as a halogen bulb but with only 1/3 the power consumption.
Another advantage of Xenon lighting is their quality is much closer to daylight than a halogen bulb. Halogen bulbs have a colour temperature of 3,200 Kelvin, while a Xenon bulb is 4,300 Kelvin. Compared to this, daylight on a cloudy day is about 5,300 Kelvin. The Xenon gas used inside the bulbs is odourless, colourless, tasteless, non-toxic and chemically inert. The gas allows higher filament temperatures and bulb temperatures can run up to 300 degrees C. We see the lights of oncoming vehicles with Xenon lights as having a bluish glow and drivers see their Xenon lights as a very white illumination.
Mercedes-Benz has added another feature into the Bi-Xenon light system – the capability to light around corners. Two sensors are used by the system to turn the headlamps up to 12 degrees in either direction. The steering angle sensor on the steering column senses which direction the driver is turning, and the vehicle speed sensor changes the angle of the headlamps in relationship to vehicle speed. At high speeds, the headlamps follow the steering angle almost instantly, but at low speeds, the headlamps react less swiftly. This prevents distracting movement back and forth on a slow twisty road or lane.
Twelve degrees of headlamp movement doesn’t sound like much but it makes significant difference in visibility. In a constant 190 metre radius turn, similar to what a driver may experience as a turn on a high speed highway, normal Xenon headlamps would provide about 30 metres of illumination. By turning the headlamp slightly, the range of illumination is extended down the roadway by about 25 metres. This is about a 90% increase in lighting.
The system does a quick self-test when the headlamps are first turned on. The automatic levelling system raises and lowers the light beam and then settles in the level position. Then the headlamps are cycled left and right before stabilizing in the centre position. To outside observers, it appears as if the headlamps are doing a little dance.
The Bi-Xenon headlamp system is only one of Mercedes-Benz active safety systems, but it is one that can allow drivers to avoid many problems on a dark winding road.