Those bright bluish headlamps that really light up the road are now being used on more and more late model vehicles. For the 2005 model year, 95 vehicle models are now factory-equipped with Xenon headlights, also known as "High Intensity Discharge" (HID) headlamps. That's a 25% increase over the 75 models that offered these unique headlamps in 2004. Applications include Audi, BMW, Cadillac, DaimlerChrysler, Ford, GMC, Honda, Jaguar, Lexus, Lincoln, Mercedes, Mitsubishi, Nissan, Porsche, Toyota and Volkswagen, Volvo.
HID headlamps were first introduced in the mid-1990s in Europe and Japan on a handful of high end luxury cars. The first domestic application was the 1995 Lincoln Mark VIII. The growth of this technology has been slow because of its high cost. But the performance and safety advantages of this high tech lighting system are generating more consumer demand for it on mid-level vehicles as well as luxury and high-end vehicles (Nissan Altima as well as Nissan Maxima and various Infinity models, for example).
Like the name implies, high intensity discharge lighting creates a very bright light that is ideal for night time driving. Though the color of the light is often perceived as having a bluish tint when viewed at night, most of the light that is produced by HID headlamps is actually very close in color to natural noontime sunlight -- though some of the light produced is also in the blue and ultraviolet spectrum. Halogen headlamps, by comparison, are more yellowish in appearance but are brighter and whiter than older incandescent style headlamps.
The near-white light produced by HID headlamps improves visibility and makes it easier to see distant objects.
The color of light can be measured in "degrees Kelvin," which refers to the "temperature" (shade) of light. Natural sunlight at noon is 4870 degrees K. Light produced by a HID xenon bulb is 4100 degrees K. Light from a standard halogen bulb is 3200 degrees K, and that from an ordinary incandescent bulb is 2800 degrees K. The lower the temperature rating, the more yellowish the light appears.
Blue-white light is better for visual perception, but yellow light is actually somewhat better for reducing glare in fog, rain and snow (that's why fog lights are yellow).
The xenon bulbs that are used in HID lighting systems also produce three times the light output of standard halogen headlamps (3000 lumens versus 1000 lumens), and require less energy (35 to 42 watts versus 55 watts). This is possible because HID lighting systems work like a vapor-filled street light or metal halide lamp. HID bulbs typically produce 71 lumens of light per watt compared to 18 lumens of light per watt for standard halogen bulbs.
HID lighting systems use a special quartz bulb that contains no filament and is filled with xenon gas and a small amount of mercury and other metal salts. Inside the bulb are two electrodes separated by a small gap (about 4 mm or 3/16th inch). When high voltage current is applied to the electrodes, it excites the gases inside the bulb and forms an electrical arc between the electrodes. The hot ionized gas produces a "plasma discharge" that generates an extremely intense, bluish-white light.
CAUTION: Once ignited, the pressure inside an HID bulb builds to over 30 atmospheres due to heat (up to 1500 degrees F inside the bulb!). This creates a potential explosion hazard so do not attempt to power a HID bulb outside of the headlamp assembly to "test" it. Also, the bulb must be in a horizontal position when it is on, otherwise it may overheat and fail.
Like street lamps and fluorescent bulbs, HID headlamps require a high voltage ignition source to start. It typically takes up to 25,000 volts to start a xenon bulb, but only about 80 to 90 volts to keep it operating once the initial arc has formed. The normal 12 volts DC from the vehicle's electrical system is stepped up and controlled by an igniter module and inverter (ballast), which also converts the voltage to AC (alternating current) which is necessary to operate the HID headlamps.
The ballast adjusts the voltage and current frequency to operating requirements. The AC ballast frequency is usually in the 250 to 450 Hz range.
Power to the HID system is usually routed through a relay and fused at the power distribution center.
When HID headlamps are first turned on, the light appears more bluish but quickly brightens as the bulbs warm up. On most applications, the HID headlamps are only used for low beams (conventional halogen high beams are used). But on some of the newest HID systems, the position of the shielding around the bulb changes position to provide both high and low beams.
Because there is no brittle filament inside a xenon HID bulb to break or burn out, the headlamps typically last up to three times longer than halogen headlamps (3000 hours versus 1000 hours of continuous operation, which is equivalent to 5 to 10 years of normal driving).
One way to tell if a vehicle is equipped with HID headlamps is to look at the outer lens cover. If the headlamps are HID, the markings D1R, D1S, D2R or D2S will be displayed on the lens. These are the four basic types of HID bulbs that are used in HID lighting systems. The bulbs are long and narrow (10 mm in diameter) with an external supporting wire that connects to the top electrode inside the bulb. The bulb also has an inner tube where the arc is formed.
D1S and D1R bulbs have a large rectangular igniter module in the base of the lamp. D1R bulbs have black masking for headlamp systems that use reflectors to direct the beam. D1S bulbs are for headlamps systems that use a light shield to direct the beam.
D2R and D2S bulbs do not have an igniter module in the base. D2R bulbs are for reflector systems and D2S bulbs are for shielded systems.
In recent years, halogen bulbs have also been upgraded to produce better lighting performance. Xenon gas has been added to the gas mixture inside some halogen bulbs to improve light output, and the bulbs have been given a blue tinted coating so the light produced by the bulb will have a similar appearance to HID headlamps. These special halogen bulbs are a good upgrade for replacing conventional halogen bulbs, but they are still halogen bulbs with a standard filament that operate at 12 volts DC. These are not high intensity discharge bulbs and do not produce the same intense bluish-white light that true HID headlamps produce. Nor do they provide the extended life or reduced current requirements of true HID headlamps.
Blue tinted halogen bulbs also do not change the beam pattern of the headlamps. True xenon HID headlamps, by comparison, typically provide significantly better foreground and side lighting because the headlamp reflectors and lens are optimized for this type of lighting.
There are also aftermarket HID headlamp conversion kits that can be installed to replace standard headlamps. Such kits include the required igniters, ballasts and HID xenon bulbs. But some of these kits are not approved for highway use and are for off-road use only.
If you need a replacement HID bulb, be warned that some of these bulbs cost up to $200 or more each at a new car dealer! Many auto parts stores sell the exact same bulbs for much less, and have bulbs to fit most applications.
If a headlamp is not working, therefore, it is important to make sure the problem is the bulb and not the igniter/ballast, power relay, wiring, fuse or headlamp switch. The igniter/ballast and relay can be replaced separately depending on the application. On vehicles that use the D1S or D2S bulbs, the igniter is in the base of the bulb and the ballast is a separate component.
CAUTION: HID headlamps operate at high voltage so caution must be used to avoid electrical shock, burns or electrocution! Make sure the headlamps are off and never service the headlamps in wet conditions. Also, do not touch the ballast when the system is operating (the ballast gets hot!).
If you disconnect the battery (recommended) before working on the HID system, use a 9 volt battery backup to preserve the PCM and other electronic memory settings.
Also, use the same precautions when handling HID xenon bulbs as conventional halogen bulbs. Do not touch the quartz bulb because the oils in your skin can cause the bulb to crack and fail almost immediately. Considering how expensive these bulbs are, that's one mistake nobody wants to make -- not even once. Wear gloves or handle the bulb by the base only.
What To Do If Only One HID Headlight Is Working: Swap the "good" bulb that is working on the other side to the headlamp that is not working. If the headlight now works, you know the bulb you removed was bad and needs to be replaced. If the headlight still does not work, try swapping the "good" ignitor module on the other side to the side that is not working. If the headlight now works, the problem was a bad ignitor, not the bulb. You need to replace only the ignitor and not the bulb. If the headlight still does not work, you have a wiring fault such as a loose ground connection, a bad wiring harness at the headlamp housing, or a corroded bulb socket.
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* If an HID bulb in a vehicle has failed prematurely, check for a possible vehicle manufacturer recall. Some 1997 Lincoln Mark VIII and 2003 Lincoln Navigators have been recalled for defective HID headlamps.
* If headlamps fail to illuminate, refer to a vehicle wiring diagram and check for battery voltage to the igniter/ballast module when the headlight is turned on. If there is no voltage or the voltage is less than 12 volts, check the battery, battery cables, wiring, headlamp switch circuit, fuses and relay in the power distribution center.
* If you accidentally touch the glass portion of the bulb, use rubbing alcohol to gently clean the bulb. Allow to the bulb to completely air dry before it is installed. There must be no trace of skin oil on the bulb, otherwise it will crack and fail when it gets hot.
* Make sure replacement bulbs are properly installed and locked in place before reconnecting the wiring and turning the headlamps on. Accurate bulb placement is essential for proper beam focus and cooling.
* If a vehicle has a cracked or damaged headlamp lens cover, the lens cover or headlamp assembly should be replaced. Water leaks and/or dust may contaminate the HID bulb and cause it to fail.
* If a vehicle has collision damage and a HID headlamp assembly is being replaced, carefully inspect the wiring before reconnecting the wiring or turning the headlamps on. A short could damage the igniter/ballast module.
The National Highway Traffic Safety Administration (NHTSA) is targeting high-intensity discharge (HID) conversion kits for enforcement actions. NHTSA has concluded that it is impossible to produce HID conversion kits (converting a halogen system to HID) that would be compliant with the federal lighting standard, Federal Motor Vehicle Safety Standard (FMVSS) No. 108. The noncompliant kits frequently include a HID bulb, a ballast, an igniter, a relay and wiring harness adapters. The NHTSA believes this equipment presents a safety risk to the public since the kits can be expected to produce excessive glare to oncoming motorists. In one investigation, the NHTSA found that an HID conversion headlamp exceeded the maximum allowable candlepower by over 800%.
Under FMVSS No. 108 Section S7.7 (replaceable light sources), each replaceable light source for headlamps must be designed to conform to the dimensions and electrical specifications for the headlamp source it is intended to replace. For example, if an HID kit is marketed as replacing an H1 light source, then it must match the H1's wire coil filament size and location, the electrical connector size and location and the ballast design for use with an H1 light source (which is impossible since there is no ballast). Consequently, companies that are manufacturing HID light sources (e.g., D1S, D1R, D2S, D2R, 9500, etc.) with incandescent light source bases (e.g., H1, H3, H7, H8, H9, H11, H13, HB1, HB2, HB3, HB4, HB5, etc.) should be aware that this light source design would not be one that conforms to FMVSS No. 108, and could not be imported and sold in the United States without violating Federal law. (The importer is treated as the manufacturer and subject to the same fines and penalties that apply to a domestic manufacturer.)
NHTSA has also determined that a commonly used disclaimer "for off-road use only" has no legal meaning and is not recognized by the agency as the manufacturer, importer and retailer are not in a position to control use once a product has been sold. Any equipment offered for sale which is covered by FMVSS No. 108 (headlamps, taillamps, side markers, etc.) must comply with the standard.