HIGH INTENSITY HEADLIGHTS

NEW XENON LIGHTS ARE HERE

 

Xenon & HID

 

   High intensity discharge lights, also known as HIDs or xenon lights, are starting to appear on many upscale cars, and a few SUVs, too.  HID headlights are expensive, but those who have them think they're great.

   That opinion isn't shared by many who have faced an HID-equipped vehicle at night.  This issue of AUTOgram examines the technology behind this new type of headlight and separates fact from fiction about those strange blue lights.

 

Headlight Basics

   The first electric headlights on cars were incandescent bulbs placed behind a glass diffusing lens.  They weren't very effective and didn't last very long.  Next, came the sealed beam, which enclosed the high and low beam filaments in a sealed glass assembly filled with an inert gas.

   Sealed beams were first available only as large round lamps, but were later offered in the then-trendy low-profile rectangular lamps.  Good as they were at the time, incandescent headlamps were limited by their design.  Over time, the tungsten filament evaporated and eventually failed.  Compounding the problem, the vaporized tungsten condensed on the lamp's glass, coating it with a  black film that progressively reduced light output.

 

Halogen Lamps

    Then came Halogen lamps.  Halogens are still incandescent lamps, but their glass enclosure is filled with a halogen gas, usually bromine or chlorine.  A chemical reaction between the halogen gas and the tungsten slows down filament evaporation and prevents deposits on the glass.  The result is a brighter light, longer life and lower power consumption.

    First available only as sealed beam units, halogens are now offered as replaceable bulbs that fit into a wide variety of headlight shapes, with some very sophisticated reflector designs and impact resistant clear plastic lenses.  Halogen lamps are still the choice of virtually every automaker, because they work well, are economical, and allow wide latitude in creating a shape that blends into the vehicle's design.

    However, the limits of halogen lamp technology were reached with the introduction of the premium halogen lamp.  It produces 30 percent more road light than the standard halogen lamp, but further opportunities for better lighting required a different technology.  The gas discharge lamp was the answer.

 

    High Intensity Discharge 

 

    Incandescent and halogen lamps produce light when an electrical current flows through a tungsten filament, causing it to turn white-hot, producing light.  Gas discharge lamps use a totally different technology.  They produce light when a high-voltage arc jumps between two electrodes that are surrounded by a special gas, like xenon.  The arc causes the gas between the two electrodes to ionize, making it a conductor.  Current passing through the ionized gas produces a brilliant light.

    Automotive gas discharge lamps are called high intensity discharge lamps, or HIDs, because to the intense white light produced by an electrical discharge.  HIDs are also called xenon lamps, referring to the gas inside the lamp.  

    All gas discharge lamps need a high-voltage pulse to create the initial arc after the gas ionizes.  HID systems are no exception, and use an electronic starter for quick ignition, and an electronic ballast to limit current after the arc is established.

 

Lincoln First in 1996

    Model year 1996 marked the first use of HID headlamps on a production car from one of the big-three domestic automakers.  The Lincoln Mark VIII incorporated a four-lamp headlight system with two lamps on each side.  Low beam illumination was accomplished with HIDs in the two outboard positions.  The two inboard lights for high beam used halogen capsules with a complex reflector.

 

Blue Lights?

The color of the light source is expressed as its color temperature.  As the color temperature increases, the light emitted will run through a scale from dark red, red, orange, yellow, and white, to light blue.  The higher the temperature, the whiter the color.

Xenon HID light sources for automtive use are rated at 4000-4500° K, while halogen lamps are rated around 3200° K.  As a reference, natural daylight is rated at around 4500-5000° K.  

    Although HID lights appear blue, their light is in fact, not blue, but white, falling well within the international specification for white light.  The light only appears blue in comparison to the warmer, more yellow light produced by halogen lamps.  It clearly appears white in comparison to daylight.

    Technically, it would be possible to make HID lights appear the same color as halogens, but that would lead to substantial loss of light output.

    The distinctive light color of HID lamps is highly effective in stimulating the reflective paints in road markers and signs, for better night time visibility.  HID lamps are more efficient at converting electrical energy into light, producing three times more lumens per watt than halogen lamps, with 40 percent less power consumption, and a four-fold increase in useful life.

 

  Lights That Irritate

 

    While it seems unlikely that anyone would complain about daylight, a few drivers object to what they perceive as glare from oncoming HIDs.  There are several possible explanations for these complaints.  Under normal circumstances, drivers look straight ahead.  However, the conspicuous color of xenon light makes drivers more inclined to look at HID lights.  The same phenomenon was experienced during the introduction of halogen headlamps in the sixties.  In those days, people also spoke of "that irritating white light".

    Therefore, the introduction of xenon headlamps will entail an adjustment period, similar to that needed during the introduction of halogen lamps, a third tail lamp, and the transition from yellow to white headlights in France.

    However, research has shown that the apparent source luminance and size are major parameters in discomfort glare.  Therefore, if the size of the headlight source is reduced, requiring higher luminance in order not to change the amount of emitted light, discomfort glare will increase.

    Since HID lamps produce light through a smaller opening in the front of the vehicle, the luminance will be higher than for a comparable lamp with a bigger surface.

 

Research Needed

    Apparently more research is needed.  Preliminary results from a study under way by the AAA foundation for Traffic Safety indicate that "the extent to which glare is a problem for night driving is not easily quantified.  In the absence of official statistics or other scientific date, evidence of a glare problem is almost entirely based upon subjective reports, most of which are anecdotal."

    "There is no doubt that the number of drivers complaining about glare is increasing, but the age of the driving population is also increasing.  While this does not negate glare as a serious issue, without good data there is no way of knowing whether the older drivers having problems with glare are those drivers with the most exposure to glare situations, or whether they are older drivers who have visual problems even in the absence  of glare."

 

  Regulations

 

    All headlights, including HIDs installed as original equipment by auto manufacturers must meet federal regulations as defined in 49CFR571.108.  Further, the international regulations that govern HIDS have three conditions that  must be met:

    These three conditions, together with the extensive life span of the xenon lamp, greatly reduce the risk of incorrectly aligned headlights.  The use of halogen bulbs entails a much higher risk

 

Why So Expensive?

    On a typical upscale new car, HID headlights will cost between $500 and $1,000.  That's because HID lights are not simply a new type of lamp, but a whole system consisting of:

    As soon as HIDs achieve wide-scale application, the price will certainly drop.  But don't expect to see them everywhere.  At best, HIDs will continue to be substantially more expensive than halogen headlamps.  HIDs should not be viewed as a replacement for halogen lamps, but as a hi-tech system for the improvement of night visibility and the comfort of drivers.

 

  Converting to HID

 

    Conversion kits are available in the aftermarket.  Kits include control ballasts, ignitor units, HID lamps, wiring, and instructions.  They aren't cheap.  Expect to pay about $1,000 for a kit that fully corrects the light pattern.  And, it isn't as simple as replacing a stock lamp with a xenon lamp.  

    Standard 12V automotive power sources are incompatible with the HID light source.  Standard halogen lamps run at 12V, while HID lamps operate on approximately 25,000V and require a surge of several amps to start up.

    The additional hardware that comes with the kit is needed to convert a car's 12V power source to drive the HID system.  The connector is also totally different from any automotive halogen lamp connector.

    HID conversions can generally be installed in any car that uses a headlight design where the lamp can be replaced independently of the headlight assembly.  Beam pattern-correct HID conversions can be done only on headlights that use a lamp that satisfies all of the following:

    If a headlight has a dual filament lamp (low and high beams combined into one lamp), a conversion may still be possible, but it may not be possible to correct the beam pattern.

    Further, high beams may have to be sacrificed.  That's because HIDs are low-beam-only systems.  Most factory installed HID systems in use separate lamps for low and high beams, with the high beams being standard halogen lamps.  HIDs are not suitable for high beams because initiation of the arc in the lamp creates a slight delay between applying power and getting full light output.  The delay is most noticeable in instances where you need to flash your high beams.  A few manufacturers use complex systems to optically tilt the high beam for low beam operation, and recent advances in system design have demonstrated that high beam HIDs will soon be available.

 

Legality of Conversions

    A well-done conversion job may be legal in theory, because it uses DOT-compliant lamps, projecting through DOT-compliant lenses.  However, aftermarket (non-factory) HID conversions are not legal for use on public roads or highways in the United States, and their use should be restricted to off-road and show-car use only.

 

Imitation HIDs

    Several lamp manufacturers sell "xenon" lamps that are a little brighter than standard halogen lamps.  Since they are still halogen lamps, they have the yellowish tint, rather than the blue-tinted white appearance of HIDs.  When compared side-by-side, the difference is obvious.

    Just because the word xenon appears in a lamp's name doesn't mean it's an HID.  And, if the replacement lamp sells for around $10, there is no way it can be the real thing.  

    Don't be fooled by color either.  Halogen lamps with the word "blue" in their names are being marketed to those who want the trendy appearance of HIDs , but don't want to pay the price for the real thing.  These imitation HIDs are really standard halogen lamps with a bluish coating applied to the glass surface.  As such, they produce less light output and are poorer performers than comparable standard halogen lamps.

 

  Intense Scrutiny

 

    As HID lighting systems continue to proliferate in the marketplace, government regulators are stepping up their scrutiny of this relatively new hi-tech development.  Several studies regarding the effects of HIDs and other lighting systems are under way--results will be reported here when they are available.

 

Comments and suggestions from readers are

always welcome.  Call or write:

David Van Sickle

Director, Automotive and Consumer Information

AAA Public Affairs

1440 New York Avenue, Suite 200

Washington, D.C. 20005

202 942 2079