Headlight systems descriptions:

What are the names of the 3 different headlight types?

  • Parabolic: The light source hits a parabolic reflector that will determine the main focus of the beam. Then the front glass will dispurse the ligth more to each side. Ie. Mercedes up until model year 2000.
  • Free form: Same as parabolic, but front lens is clear. Ie. Volvo V70
  • Ellepsodial: Light source hits a parabolic reflector, gets horisontally cut off in the first focal point, then projected back straight again with a curved lens. Ellepsodials also goes under the name projector headlights.

    Reflector design is a common description of Parabolic and Free Form.

    What is the difference between projectors and reflector design?

    Parabolic: 27%
    Ellepsodials, 1st gen (found on early 90s BMW): 36%
    Free form: 45%
    Ellepsodials, 2nd gen (found on late 96+ Audi, BMW): 52%
    There has been a trend that more and more wehicles go away from the traditional parabolic headlamp. The thick glass that are needed makes it a looser in the game of efficient lighting. It seems like the majority of auto manufacturer selects ellepsodials. They werent up to par in the first generation. The lower 180 degrees of the bulb output were practically not getting out of the housing. The second generation is designed with another focal point to increase efficiency.

    BEAM CUTOFF). Projectors create a much sharper cutoff than reflectors. Allthough some parabolic reflectors can create pretty good cutoffs a projector will always be better. This has the main advantage that projectors can be aimed higher than reflectors because no stray light (above the cutoff) will exist to cause glare to oncoming drivers. This is especially important with high intensity light sources like HID and the new HIR halogen bulbs.

    UNIVERSALITY). Projectors can be designed to be easily switchable from left drive to right drive beam patterns without loss of light. This usually done by turning the reflector housing in reference to the shield and you get the full 'opposite' beam pattern. UK needs this ability to drive legally on the continental Europe. This is why some cars for the UK market have projectors where the rest of the world don't.  With a parabolic reflector, the 'kick up' part of the lens has to be taped up (so you lose the kick up completely).

    VERSATILITY). Projectors are normally not used in combined high/low beam setups. Clearly,  it's possible to have a moveable shield and this is just what happens with "bi-xenon projector" setups, but this would be very costly in a econo car with halogen setup. A regular H4 or 9007 application is much more cost effective.

    What is the difference between Xenon/HID systems and conventional halogen systems?

    Xenon/HID systems use different principles in the creation of light than halogen. HID bulbs contain a small capsule with a mixture of xenon gas and halide salts that aid in the creation of a powerful light source that is generally 3 times brighter than halogen bulbs. Halogen bulbs use a filament that creates light from basic ohmic resistance across a filament. While halogen bulbs runs directly from the cars 12V system, HID bulbs require a complex ballast that can supply accurate high voltage.

    Color Comparison pitures:
    In Kelvin (Source: PIAA)
    Somewhat real life (Source: Bell Of HID)

    What is the beam difference between ECE, DOT, JDM, and harmonized headlights?

  • Headlights following US standards are labled DOT. Note the increased illumination of overhead signs, which also results in higher glare levels for oncoming drivers. Maximum allowed illumination is 28,000 candela.
  • Headlights following european standards (ECE) are labled E followed by a number. Note the much lower glare levels above citoff and sharp horisontal cutoffs. Maximum allowed illumination is 38,000 candela.
  • Harmonized headlights are labled (example:) E4 DOT. They can legally be used on both continents, but a true ECE headlamp will always have higher output.
  • Headlights following japanese marked (JDM) has a vertically mirrored ECE pattern, and is for driving on the left side of the road only.

    See regulations section for more details.

    How does a OEM Bi-Xenon system work?

    Very simple, Bi-Xenon means that both high and low beam is created by the same HID bulb. A Bi-Xenon system can be based on reflector and projector design. The latter one is the simplest. Hella has a Bi-Xenon system that has a moveable shield inside a projector unit. This is acomplished by using a spring loaded solenoid (just like in power door locks) or servo motor with 2 positions. Bi-Xenon came on many cars in 2002.

    The advantage compared to a traditional projector HID low beam/Halogen high beam is that you get HID low AND high beam. Bi-Xenon systems have additional flash-to-pass separate halogen lamps. Bi-Xenons System are a step up from regular low beam Xenons, since there will be better high beams. The high beams in a HID low beam HID/ halogen high beam combination has a tendancy to be degraded to a beam cutoff softener. It is easy to get spoiled by the powerful low beam HID which makes high beams with 65W halogen almost dim in comparison. They should have been 140W high beam. Bi-Xenons gives a better long distance view when high beam is on.

    Bi-Xenons are not perfect either. Ideally, they should have made foreground lighting weaker when switching solenoids over to high beams. But that feature in non avail so far.

    See OEM HID database for cars with this option. The downside with Bi-Xenon systems and traditional low beam Xenon systems is that illumination close to the car is too bright at high speed driving. This is one of the reasons why the "Vario Xenon" system is superior.
    Do not confuse OEM Bi-Xenon system with an aftermarked "Bi-Xenon HID kit". This is described under the "HID kit" section.

    What is Distrubuted Ligting Systems (DLS)?

    The intention is to move bulb away from headlamps into a common, very powerful source. Weight will be saved because fibre optic wires are lighter than copper. Amount of bulbs will be saved. Fibre cable is terminated into a fresnel type lense which shapes the beam output. There are a number of prototypes out there, but they're still experimental. For a full-blown AFS lighting system (see further down), they'd be great, since the aiming motors would only have to move the light pipes, without moving the heavy, bulky fixtures. This would make the headlight "stylists" (and marketing people) happy too, since there wouldn't be any ugly clearance gaps between the moving part of the headlight and the surrounds.

    How does a Vario-Xenon (Hella trademark) system work?
    This is a future headlight system that will adapt to all kinds of conditions. It has varoius sensors that make headlights adapt light distrubution according to ambient light, speed, steering wheel position, and possibly GPS coordinates. A common powerful Xenon bulb is placed away from the headlights. Light is transferred through thin fibre optic cables to headlights, where they terminate in variable fresnel lenses. Rumors say that Verio-Xenon will be available during 2002 from Hella for automobile manufacturers. The future will tell if they are able to get production cost down. Volvo has been testing this system in their SCC concept car since 2001.

    What is AFL?
    The Adaptive Forward Lighting (AFL) concept was later introduced by Hella after Vario-Xenon, probably a better name and probably lower cost. It utilises a BI-Xenon projector unit to adapt to road conditions only according to speed and steering wheel position. The projector unit rotates up to +/- 15 degrees to each side.

    A second bulb and reflector will direct light 90 degrees sideways, which will help you see those dark pedestrians when you take a right turn on red. Mercury Sable, Cadillac and some other north american car models has similar function: A 25W bulb illuminates 50 degrees to the side when turn signal is on. AFL might be seen on a future Opel Vectra and Signum models, pending ECE recognition.

    What are the general options to get HID ligthing on my car?
    The options are many. When converting to HID in Halogen housings, the success rate is mostly based on how much light is actually going above the cutoff line, and how even the beam spread is, not if the glass is fluted or not. This page describes all HID upgrade options, not just the "HID bulb placed into a halogen socket" option. A reason for just choosing the best halogen available could be that you dont have time, lots of patience, planning skills and finacial priorities for going the HID route. An HID install will set you back $300 - $1800, all depending on how much tools and parts you already have. You dont know how much before you start planning.

    What differs left and right side headlamps?
    Optically, there will be no difference. Left and right beam pattern are the same. Esthetically, left and right headlamp are of course mirrored, to make the front look pretty. Internal components (ballasts, projector units) is most often mirrored as well. Contents of components are the same, but mounting tabs, connector placement and so forth, can be mirrored.

    What can I gain from having HID in low beams, compared to halogen?
    Having HID bulbs in low beams is widely used. Having a slow turn on HID bulb in a low beam application is no downside. It is solved by having the low beams come on right after engine is started, and they cannot be turned off before you switch ignition off. In general, there are only advantages, besides from higher price.

    What can I gain from having HID in high beams in a traditional open reflector based system, compared to halogen?
    1) Can use smaller reflector to achieve same or higher brightness compared to halogen.
    2) Lower energy consumption. Physically heavy and amps sucking halogen based light clusters seen on rally cars has become a thing of the past.

    1. HID bulbs do not achieve full brightness until the metallic salts in the HID capsule are completely vaporized, which could take up to a minute (or more) on some setups. This means they would not be much good for "flash to pass" signaling or extra light on demand.
    2. Decreased bulb life if turning HIDs off and back on again. Continuous use in traffic passing situations would mean many hot re-strikes of HID arc, which shortens HID capsule life and requires MORE startup current than a cold capsule, thereby putting added wear & tear on your wiring and switching components.
    3. Higher price. HID based systems costs more.

    None of the above is a problem with a OEM "bi-xenon" setup, since the high/low is accomplished thru a mechanical moving shield and/or moving reflector, and the actual HID capsule remains constantly on, with no warm-up or hot re-strike required.

    Is a bigger headlamp a better headlamp?

    A bigger diameter reflector result in that bulb sits further back and will result in more light getting reflected forward.

    Does any car use LED based headlamps?

    Per March 2003, there are no production cars using LED headlamps. However, several car manufacturers is experimenting on prototypes. The first production models is expected to reach production around 2005. A typical LED headlamp will consist of 15-50 single LEDs. Each beam will be aimed in its unique direction. With an 80 degree beam opening angle and 15 LEDs, each beam will cover 5.3 degrees.
    LED supplier
    Lumileds is probably leading the LED output race with 120 lumens from a single LED. There is no doubt that Lumileds will be one of the big suppliers of white LEDs for headlamp use. Lumileds is a joint venture of Agilent Technologies (HP spinoff company) and Philips Lighting. For now, the challenges are:

  • Getting enough lumens per dollar
  • Sufficient horisontal cutoff line to get correct glare values.
  • Getting intensity even from across beam from side to side.
  • Per summer 2003, the lowest color rating was 5500K on all high output white LEDs. This is too bluish color for current regulations.

    Mitsubishi showed their prototype with LED headlamps in 2001.
    Fioravanti Yak concept vehicle with LED headlamps was presented in Geneva in March 2002. See article and pictures on lumiled's press release.
    Audi presented their prototype car, Nuvolari quattro, with LED headlamps in Geneva in March 2003. See audiworld.com for deatils.

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    Copyright 2001, 2002, 2003 Automotive Ligthing FAQ