For the nighttime driver, headlamps are as essential to safety as brakes or quick handling. They are literally the car’s eyes: they lend the car’s face much of its personality, from the Beetle’s friendly round ones to the Viper’s beady snake-like countenance. More importantly, at night the driver will be virtually blind without them.
A Brief History of Light
As far back as 1886, cars such as the Benz already had headlights. These cars already had gas-discharge lamps, but not as we know them today. Rather, they were lanterns that burned acetylene or kerosene.
A major advance was when cars developed a complete electrical system. Originally, the electricity was limited to the ignition equipment. With the advent of the electric starter on a 1912 model, electric lights began to replace the gas lanterns.
The earliest electric light bulbs used filaments that actually became hot enough to emit light when an electric current was passed through the filament. Filaments of impregnated paper gave way to carbon and then tungsten, which burned brighter and lasted much longer. These were known as incandescent bulbs.
At Present: Halogens and Multi-reflectors
Lighting technology in most new cars is still limited to incandescent. Halogen bulbs are still classified as incandescent, because they still rely on a filament to provide the light. They are a step up from conventional incandescent because inside each glass bulb is not a vacuum but a concoction of halogen gases such as krypton. The wire glows from heat, and this excites the gas molecules enough that they also emit powerful light energy. Halogen bulbs can be up to 50% brighter than conventional incandescent, and can last up to twice as long.
Making sure all that light output is “thrown” out efficiently onto the road ahead is the job of the reflector-essentially, a paraboloid mirror. The bulb is positioned at the mirror’s focus to reflect all rays of light parallel to the mirror’s axis-that is, reflected out the front of the car. In a low beam/high beam bulb, the high beam is at the focus while the low beam is positioned a few millimeters in front of the focus, to aim the light downward. A shield incorporated in the bulb prevents reflections from travelling upward into the night sky.
Aiming is accomplished with the use of ribs and grooves of different thicknesses in the lens in front of the reflector. These act as prisms and make sure the light is aimed into the appropriate distance in front of the car, and with enough lighting at the sides too, to illuminate curbs and other objects that the driver would want to avoid.
They also make sure that oncoming drivers are not blinded by the headlamps. Due to legal requirements, American-market cars tend to emphasize this non-offensiveness, and thus have a fuzzier cutoff compared to European-market cars. Cars meant for Europe have a more aggressive headlamp approach, with a longer beam throw and a sharp horizontal cutoff, perhaps necessary due to all that London fog and Autobahn speed.
A recent innovation is the use of High-Intensity Discharge (HID) lamps, similar to the ones used in stadiums and streetlights. These systems require an ignition coil to jump-start the current to 10,000 volts to establish a bright arc of current between two electrodes. The two electrodes are enclosed in an “arc tube” together with xenon, mercury and other halides, causing the gases to illuminate. The arc tube is capped with another quartz glass outer jacket to trap heat and filter ultraviolet radiation. In contrast to stadium lighting which needs several minutes to warm up, a car’s discharge lighting only needs about 0.3 second to equal the light from a halogen bulb.
These gas-discharge systems provide more output while using up less current than halogen systems. Since they have no filament emitting lots of heat, HID headlamps can be reduced in size, which gives further advantages in aerodynamics and aesthetics.
You’ve probably seen E-class Mercedes with those futuristic blue beams of light. Those beams are closer in color temperature to natural daylight. They cut through fog and rain more efficiently than halogens, and make road signs and other cars much easier to see. Several other car companies are adopting them, such as BMW and even Ford. The downside? These systems cost about $1000 per car, and companies like Mercedes do charge about that much for the system as an added option. However, when enough models switch to this technology, the cost should go down rapidly until even economy cars will be equipped with them.
Now, you can’t insert an HID bulb into a socket meant for a halogen. The bulb shape and socket are completely different. Also, a halogen system cannot supply the required voltage. If you want to have a brighter beam, we suggest trying replacement halogen bulbs that are closer to HID in performance. We tried PIAA’s Plasma Blue (aka Super Plasma) bulbs in our test Cefiro and Accord and were impressed with the performance. They aren’t cheap at about P4000 per pair, but it’s actually worth it in terms of safety and driving comfort. PIAA claims a light output double that of the original bulb, in addition to a much higher color temperature. The installation in the Cefiro was particularly rewarding. The beam now had a longer throw: illumination in near and mid-distances, as well as long-distances on high beam, was indeed much-improved. We suspect the pre-facelift (1998-99) Cefiros sold here were European spec, because the beam cutoff is quite sharp. The Accord, we were surprised to find, did not show such a dramatic improvement, maybe because its conventional halogen system was already quite bright. Still, the light now has a purplish-white cast, and is quite closer in color to solar light.
The Swinging Future and the Invisible Made Visible
Of course those engineers never leave well enough alone, and a lot of new technologies are on their way.
One innovation was actually initiated way back in the 1950s by Tucker in his Torpedo model. The Torpedo had a central third headlight with a reflector which swiveled left to right, as the driver turned the steering wheel. That way, the third headlight was always aimed at where the driver wanted to go, not where the car was presently pointed. Observe where your headlights are aimed as you turn a corner or curve and you’ll appreciate the idea. BMW is trying out such a swiveling-reflector system.
Bosch is working on a system that uses multiple bulbs and reflectors within the headlight assembly, each illuminating according to driving conditions. For example, a wide, short-throw beam would automatically turn on when driving city streets and long-throw high-intensity beam would switch on during highway driving. A set of cornering lamps could be included within the light cluster. Electronic connections to the car’s speedometer or even Global Positioning System can make such programmed lighting possible.
The ultimate lighting technology will go beyond visible light itself, to the infrared or ultraviolet, or even radio waves. Volvo has been experimenting with ultraviolet beams projected far beyond the main headlights’ reach. These of course do not blind oncoming drivers but cars will need fluorescent paint or markings to reflect the beams. As a bonus, moose, a serious driving hazard in native Sweden, already have fluorescent hair and will show up in an ultraviolet beam.
At the other end of the spectrum, the 2000 Cadillac De Ville is equipped with an infrared system. The infrared emitter is positioned on the car’s grille. The resulting image is projected in letterbox format on the lower portion of the windshield. The nightvision system helps the driver see through the glare of an oncoming car’s headlight, and detect obstacles which would not have shown up in a normal headlight’s beam.
As with most things in the automobile, the headlights’ form must follow function. The driver, the brain of the car, needs the visible spectrum of light. Radar and other invisible devices will probably never take the place of a set of bright lights at the car’s front. Cars will therefore have those expressive eyes for as far as the foreseeable future.
By Redline | Photos by Tamago
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