The Past: What most cars in North America currently use
Car lighting systems have evolved slowly. Early cars simply carried over the carbide brass lanterns and incandescent lamps used on carriages. The first truly innovative development, in the early 1920s, was the dual filament or “Duplo” lamp. The early 1950s saw the introduction of the first asymmetrical lamp, the “Duplo-D,” with a low beam and a high beam in a single sealed housing.
The next big development, the single-filament halogen bulb, became available in Europe in the mid-1960s. These new, longer-lasting lamps took less energy than incandescent, and provided 50% more light. Dual- filament halogen lamps developed in the 1970s are used today in most US cars.
Until 1975, all US headlights had to be round, non-halogen, U. S. Department of Transportation- (DOT)-approved sealed beam units, either two large dual-beam bulbs or 4 smaller single-beam units. From 1975 on, the DOT made provisions for rectangular sealed-beam bulbs, in the same layout as the round ones. In 1985, under pressure from consumers and automakers, the DOT finally adopted its current European-based lighting standard, which allows for halogen lamps and non-standard headlamp shapes. Most automakers have moved to composite lamps that blend with the styling of the vehicle, still within the DOT rules.
Headlights remain one of the most highly regulated systems on any vehicle. And unfortunately for North Americans, the existing European standard, legal but not mandatory in the US, is still years ahead of current minimum DOT regulations. Perhaps some of the high-tech European models will pressure domestic automakers to let us “see” into the 21st Century.
The Present: What’s available, though not common
High- and Low-Pressure Gas Discharge Systems – Halogen lighting uses gases, either xenon (for headlights) or neon (for brake or tail-lights), to produce a highly concentrated light very well suited to automobile lighting. In a gas-discharge system an electric spark jumps a gap (arc) inside a capsule filled with gas. The arc produces significantly more light than a glowing filament, providing better visibility not only for the driver of a xenon-equipped vehicle, but for people following a car with neon brake and tail-lamps. Even among halogen lights, different technologies.
The first production vehicle to contain both a high and a low-pressure gas discharge lighting system was the 1997 Lincoln Mark VIII. Its distinctive high-intensity discharge (HID or high-pressure) front headlights produced 2.7 times more light than standard halogen bulbs and its low-pressure neon gas rear lighting made the car visible to vehicles following miles down the highway. A 48-inch neon tube across the rear of the Mark VIII improved both the visibility and the reaction time of the center high-mounted brake lamp. At the 1999 IAA International Automobile Exhibition in Frankfurt, Siemens exhibited a show car with xenon headlamps, yellow neon front-end turn signals, a red neon center-mounted rear brake lamp, and LED brake lights, tail lights and turn signals. The new BMW Z8 roadster comes with yellow neon lighting in its signal lamps and red neon in the center high-mounted brake light.
High-pressure gas-discharge systems (xenon) – The high pressure XENON lamp is ideal for automotive head lighting systems. It offers more than twice the amount of light of halogen for half the energy and a better quality of lighting. Designers are given the flexibility to develop entirely new headlamps that give a car its own character. Many high-end car manufacturers like Acura, Audi, BMW, Cadillac, Jaguar, Lexus, Mercedes-Benz, and Porsche have incorporated XENON systems into their top-of-the-range models.
European regulations require that the headlamp leveling of HID-equipped cars be linked to the suspension system of the car so the lamps don’t glare into oncoming traffic when the rear of the car is loaded down or the car is heading uphill. Xenon-equipped European vehicles imported to this country all have self-leveling systems. American regulations don’t require auto-leveling. It remains to be seen whether US automakers will install self-leveling systems if not required to by law (my guess is they won’t).
Low-pressure gas-discharge systems (neon) – Low-pressure gas-discharge lamps, which can be manufactured in almost any length and shape, offer entirely new lighting opportunities for automotive designers. One lamp can serve multiple functions, simply by adjusting the lighting levels. They are significantly brighter than an equivalent incandescent lamp and consume only about 60% of the power. They also last three times as long and the absence of a filament means that they are highly shock-resistant. The recently introduced neon brake light reacts much faster than an incandescent lamp. Whereas conventional filament brake lights switch on in about 200 milliseconds, a low-pressure gas-discharge light will reach full intensity in less than a millisecond. This represents a reduction in braking distance on the road of almost 17.4 feet for a car traveling at 60 mph. This could mean the difference between a safe stop and a collision. The lifetime of these new lamps is around 2,000 hours or some 800,000 braking operations. This more or less represents the life span of a typical car, which means these lamps will probably never need replacing. Available in different colors, low-pressure gas-discharge lamps can be used for other lighting purposes in the back of the vehicle, such as fog lights and indicator lights (BMW Z8).
LED Brake Lights & Turn Signals – Approximately 40 percent of the European automotive market uses LED high-mount brake lights — more than 90 percent of which are manufactured by Hewlett-Packard. In the United States, more than 25 percent of high-mount brake lights use LEDs, with an increasing number of new vehicles employing LEDs for turn, tail, and stop functions, as well as for front turn signals. The 2000 Cadillac DeVille uses Hewlett-Packard LED technology for its entire tail-lamp and brake light assemblies. “LED advantages such as reliability, design flexibility and safety have been embraced by the automotive industry since the 1980s…. now we are seeing many innovative new designs for full combination lamps — those that combine turn, tail and stop signals.” says Mike Holt, automotive program manager for HP’s Components Group. The LEDs, which emit true red-orange and amber colors, are not dependent on lens color. This eases the red and amber lens-color restrictions of incandescent signal lamps and designs.
The Future:
Brake-force-dependent Rear Lighting – A traffic safety innovation designed to reduce the incidence of rear-end collisions by warning motorists when cars ahead of them are making panic or sudden stops is under development by Hella. It was displayed at the Society of Automotive Engineers SAE 2000 World Congress at Cobo Center in Detroit. The novel rear-lighting system consists of several lighting elements, which are progressively activated according to the amount of pressure applied to the brakes. The more brake force applied, the more segments of the lighting system are illuminated. The power-dependent light signal gives following motorists an indication of traffic flow and driving conditions ahead. Light braking pressure will illuminate one segment of each brake light. With increased pressure, additional segments are lighted. An emergency stop would activate all segments of the system, alerting drivers that are following of the need to take action to avoid a rear-end collision.
Single Source Lighting Systems – In these currently experimental systems, light is sent from the light source via optical fibers to the side mirrors which double as headlamps. A series of optical fibers to the front of the car provide excellent fog lighting. These applications have become possible using single source lighting. Fascinating opportunities await car designers in the near future. You can easily imagine switching optical fibers independently from one another, using intelligent control electronics. The headlight pattern is not limited to separate, overlapping beams, but can be easily adapted to provide optimum visibility over a wide range of driving conditions. The beams can also be made to turn left or right, to follow the turns the driver is making. These options contribute even more to safety on the road and to more comfortable driving. Optical losses in the system, caused in particular by absorption in the glass fiber and coupling/decoupling losses, are rather high. This rule out all but the strongest and brightest light sources. Research has shown that XENON lamps provide sufficient luminous energy in a distributive system to meet all current main-beam requirements, so look for single source lighting to appear on production models in the next five years.
Lighting System Maintenance
Cleaning – is the most effective maintenance that you can perform on your lighting system. Drivers in the rust belt are already aware that wintertime driving wreaks havoc on a cars finish and overall appearance. The front-end of a vehicle is exposed to the brunt of winter road maintenance by-products. Salt, sand, and soot can quickly cover your headlamps, rendering them virtually useless. Dirt and road buildup on a head-light lens can cut light output by 40% or more. At every opportunity, you should stop your vehicle and wipe off your head-light lens with whatever’s available. Service stations and rest tops are the obvious place to pull over, however a gentle scrubbing with a snowball can be just as effective, especially if you’re in the middle of no-where. Don’t forget your tail lights and turn signals.
Don’t think that you’re immune to headlight scrubbing if you live in the south. Insect carcasses can have a dramatic effect on the beam pattern and brightness of your headlights. Baked-on insects can be especially hard to remove as well. A good scrubbing with a soft brush and soapy water will usually all but the most stubborn insect residue, which can be removed by a good bug and tar cleaner.
Condensation – Moisture inside today’s plastic headlight assemblies can collect on the inner surfaces of the lens, compromising the beam pattern, and allowing exposed electrical connections to oxidize (ending up in bulb failure). The problem is usually exacerbated by humid weather, or by driving your car through a car wash. Moisture enters the lights through the vents that allow for expansion and con-traction as the air within the light chamber heats and cools. Most composite lights are designed so that airflow sweeps away the condensation as they warm up, however if the vent tube is clogged or the housing is cracked, the condensation may never go away. Some taillights are also prone to condensation problems, if your headlights or taillights are foggy or dripping wet on the inside, read on.
Replacing – Older vehicles may have lenses made of a polycarbonate plastic which can become cloudy or yellowed with age. Roadway hazards, or the byproducts of roadway maintenance can easily crack or scratch the lenses of any composite headlight assembly. Additionally, moisture that won’t go away needs to be resolved. Have your mechanic remove the assembly in question to see if the tube is blocked, or the case is separated or cracked. Separated seams can usually be glued, however cracked lenses are illegal and the lens needs to be replaced. (Some lenses are available separately from their assemblies although most are only available by purchasing the whole thing – a $200 to $800 expense.) WARNING – Never touch the glass portion of a halogen bulb with your fingers, handle the bulb by its plastic base. Oil from your fingers will contaminate the bulb and cause it to crack or fail prematurely.
Aiming – Experts estimate that 50% of the vehicles on the road have improperly aimed headlights. In most states, checking the aim of your headlights is part of the state inspection procedure. If it’s not, it should be! Many new vehicles come equipped with a liquid-filled level on the back of each light to facilitate its correct positioning, older ones can be adjusted by using knobs or screw assemblies (adjusters). If your car is more than a few years old, chances are good that the adjusting screws have oxidized and are frozen in place. Because of the chances for permanent damage, I strongly suggest you take your vehicle to your mechanic if you are unsure of how to aim your lights, or if the adjusting screws are frozen.
If your adjusters are in good working order, the actual aiming process is quite simple. Locate an absolute level surface adjacent to a light colored flat surface, either a wall or a garage door. Park your vehicle perpendicular to the wall at a distance of 25 feet from it, and open the hood. Put your car in park, start the engine, and turn on your low beams. While looking at the wall, experiment with the adjusters, observing which knob or screw moves the beam up and down, and which one move the beam to the left and right (some lights only offer vertical adjustment). The focal points (or hot spots) of the low beams should be aimed slightly down and to the right from the horizon line (vertical centerline of the vehicle’s headlamps) when shone at the wall (on composite lens assemblies, the high beams cannot be adjusted separately). When you’re satisfied, close your hood, and sit down in the driver’s seat and double check that you’re happy with your adjustments. If your low-beams are properly adjusted try your high beams. There should be a noticeable shift in the beam’s direction, from down and to the right (low beam), to straight ahead (high beam).
Most built-in fog lamps aren’t adjustable, but if yours are, make sure that they’re aimed low. The idea is to throw light under the fog, not into it.
Source: Smartmotorist