Headlights
Headlights began very simply as lanterns mounted on the earliest horseless carriages. As the versatility of automobiles widened, improved lighting systems were needed and the incandescent, sealed beam headlight was devised and used almost universally for decades.
The incandescent headlight consisted of a housing or assembly, a light bulb as the light source, a reflector that bounced the light forward, a protective lens or cover that focused the light beam and protected the bulb, and connections to the car's electrical system. Double filaments in the bulb allowed for a high and a low beam. The bulbs produced a yellowish beam that caused eyestrain; they also darkened and dimmed with age. This type of headlight produced a sufficient amount of directed light for the driver to see without blinding oncoming drivers, but it was inefficient because more than 70 percent of the light produced by the bulb was either lost as heat or not collected by the reflector.
The same sealed-beam unit was improved in the 1970s when the halogen bulb was developed. Halogen bulbs don't dim or darken over time, and their light is brighter and less straining. Because the headlight was a sealed assembly, a burnt out bulb meant replacing the entire headlight. This also dictated standard shapes and sizes, and round or rectangular headlights were the only available designs until about 1980. Replaceable halogen bulbs opened new opportunities in headlight configurations, and advances in plastics and fiberglass in automotive design made model-specific headlights possible. Automotive designers could create aerodynamic masterpieces with headlights that matched the design concept. Lenses could also be formed from plastic instead of glass, which aided both design and weight.
Projector-beam headlights were the next technological leap. Halogen bulbs are used in devices resembling overhead projectors. The light source is projected up and out by means of a reflector and magnifier shaped like an ellipse. The reflector is so precisely shaped that the pattern of the beam is well defined. More light is made available without increasing the load on the electrical system of the car and while creating less glare for oncoming traffic. Projector-beam headlights can also be manufactured in smaller sizes to suit automobile designs. They have been used widely since 1987.
Technical advances improve components of headlights and methods of designing them. In "Free Form" or FF systems, engineers choose the beam pattern they want the headlight to produce then use computer applications to design the reflector that will generate that beam. FF reflectors look like they are made of puzzle pieces because each piece reflects light to a particular point on the road. Because the reflector shapes the beam pattern, the function of the lens is less optical and more decorative or protective. More of the light from the bulb is captured by this precise design, however, and the FF beam has a 45 percent efficiency, as opposed to 30 percent for the incandescent, sealed-beam units and 35 percent for projector-beam headlights.
In 1995, the High Intensity Discharge (HID) system debuted in Europe and the United States. HID changes the bulb source itself. Electricity arcs from one electrode to another in xenon gas, rather like a fluorescent tube instead of a glowing filament inside a conventional bulb. A projector-type reflector produces an efficiency rating of 50 percent and dramatically reduces the electrical demand. The xenon gas produces a bluish light when viewed by oncoming cars, but the subject vehicle's driver sees a beam that is bright white. Fiber optic systems are also in development for automotive applications. Fiber optics will carry light from a single source in the vehicle to headlights taillights, and the dashboard. These systems have only been demonstrated in concept cars, but they may be commercially available by the year 2000.
Taillights demand less design attention because visibility and safety instead of complex beam design are the issues. Turn signals, reverse lights, and brake lights are coordinated by the car's electronics; hazard warning systems add the dimension of blinking sets of front and rear lights when the car is stopped and on the driver's command. Fog and driving lights project short, wide beams and long, intense beams, respectively. Fog lights help light the sides of the road during bad weather without causing glare, and driving lights (which are illegal unless they are used with high-beams) permit the driver to see more clearly and farther ahead. Both fog and driving lights are designed based on conventional halogen, projector-beam, or FF technology.
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