page_title: Headlamp
section_title: Projector (polyellipsoidal) lamps
hierarchical_section_title: Headlamp / Optical systems / Projector (polyellipsoidal) lamps
caption_attribution_description: English: Headlamp schematic (projector optics)
context_page_description: A headlamp is a lamp attached to the front of a vehicle to illuminate the road ahead. Headlamps are also often called headlights, but in the most precise usage, headlamp is the term for the device itself and headlight is the term for the beam of light produced and distributed by the device.
  Headlamp performance has steadily improved throughout the automobile age, spurred by the great disparity between daytime and nighttime traffic fatalities: the US National Highway Traffic Safety Administration states that nearly half of all traffic-related fatalities occur in the dark, despite only 25% of traffic travelling during darkness.
  Other vehicles, such as trains and aircraft, are required to have headlamps. Bicycle headlamps are often used on bicycles, and are required in some jurisdictions. They can be powered by a battery or a small generator like a bottle or hub dynamo.
context_section_description: In this system a filament is located at one focus of an ellipsoidal reflector and has a condenser lens at the front of the lamp. A shade is located at the image plane, between the reflector and lens, and the projection of the top edge of this shade provides the low-beam cutoff. The shape of the shade edge and its exact position in the optical system determine the shape and sharpness of the cutoff. The shade may be lowered by a solenoid actuated pivot to provide low beam, and removed from the light path for high beam. Such optics are known as BiXenon or BiHalogen projectors. If the cutoff shade is fixed in the light path, separate high-beam lamps are required. The condenser lens may have slight fresnel rings or other surface treatments to reduce cutoff sharpness. Modern condenser lenses incorporate optical features specifically designed to direct some light upward towards the locations of retroreflective overhead road signs.
  Hella introduced ellipsoidal optics for acetylene headlamps in 1911, but following the electrification of vehicle lighting, this optical technique wasn't used for many decades. The first modern polyellipsoidal (projector) automotive lamp was the Super-Lite, an auxiliary headlamp produced in a joint venture between Chrysler Corporation and Sylvania and optionally installed in 1969 and 1970 full-size Dodge automobiles. It used an 85 watt transverse-filament tungsten-halogen bulb and was intended as a mid-beam, to extend the reach of the low beams during turnpike travel when low beams alone were inadequate but high beams would produce excessive glare.
  Projector main headlamps first appeared in 1981 on the Audi Quartz, the Quattro-based concept car designed by Pininfarina for Geneva Auto Salon. Developed more or less simultaneously in Germany by Hella and Bosch and in France by Cibié, the projector low beam permitted accurate beam focus and a much smaller-diameter optical package, though a much deeper one, for any given beam output. The 1986 BMW 7 Series (E32) was the first volume-production car to use polyellipsoidal low beam headlamps. The main disadvantage of this type of headlamp is the need to accommodate the physical depth of the assembly, which may extend far back into the engine compartment.
caption: Projector optics, side view
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