Lately I've seen a whole LOT of talk about HID and all the things about it. I'm getting rather tired of all the hear-say being spread about, so here's the low down on HID. Kornhaus can also back me up/correct me on this as he works for Hella.
First off, HID stands for High Intensity Discharge. Unlike standard halogen lighting, HID lighting typically burns a Xenon gas at such a rate faster than the human eye can detect, hence a solid beam from the lights. HID parts include a ballast, igniter, projectors/reflectors (including dish and lense), and bulb. HID setups create a very intense, very bright light, very closely simulating sunlight during the day. The projectors/lenses create a very sharp cutoff in their beam pattern; that is there is a distinct horizontal line between light and dark. This is what prevents blinding oncoming traffic from being blinded
Again, parts included in an OE setup include ballast, igniters, projectors/relfectors (depends on the spec), bulbs, high current wires, auto-levelling mechanisms, and lense washers. Wiring starts at the ballast (which powers the bulb) connects through a high current wire to the igniter. The igniter is what starts the initial power-on of the bulb (approx 23kV of power). Sometimes the igniters are built into the ballast, sometimes on the wire between the ballast and bulb, and sometimes directly to the rear of the bulb. The bulb then sits inside the projector and the projector inside a large clear plastic housing. Recently auto-levelling and lense washers have come out. Auto-levelling is when a small motor controls the up/down aim of the cut off line when there is a load in the rear of the car (weight in back of the car pushes the headlight beam up). Lense washers are mounted on the outside of the car to keep the large clear lenses clear. I'm not positive if auto-levelling or lense washers are required for legality, but I've seen cars with and without both technologies (BMWs have both, some Acuras have neither).
HID is legal. It comes on high end vehicles such as Beamers, Mercades, Audis, some Volkswagons, etc. HID is legal when the high output bulbs are paired with a proejctor/reflector. HID is ILLEGAL and UNSAFE when a high intensity bulb and ballast are fitted inside a halogen bulb housing (IE Car toys HID kits; also found on ebay). These kits are labeled as "for off road use only" as the light emitted from this setup can blind drivers. The way around this (though technically still illegal) is to take a true HID setup (such as OEM from BMW) including the bulbs, ballasts, and projectors... and then fit the projectors into the halogen housing.
The DOT recently passed a law stating that any alterations to headlights in such manner as not offered from the factory are illegal. Fitting an HID bulb into a halogen is illegal. Technically so is fitting an HID bulb and projector into a halogen housing. Police are not thoroughly and regularly enforcing the HID laws passed by DOT, therefore you could get away with either setup. The problem in using a xenon bulb in just a halogen housing is that there is no distinct cut-off line as there is with projectors. In a halogen housing, light is emitted all over the place with no definition, creating a problem in blinding oncoming traffic.
There are multiple specs and manufacturers for HID setups. Bosch, Hella and Valeo are a few mfrs, each with their own generation of parts. There are also multiple specs, H7, D1S, D2S, etc etc. Sometime specs work interchangeably, though it isn't wise to rely on parts being inter-changeable. The best and safest way to create a semi-legal/working HID setup for your non-HID car is to purchase parts from a single spec/platform and retrofit a projector into your housings.
Xenon technology, when first becoming popular in the late 90s, only provided light as a solution for low beams. Since then a technology has come out called Bi-Xenon, which provides high and low beam light from a single bulb/projector. The way this is accomplished is by taking a projector housing and mounting a small flap/selenoid near the bulb. This flap blocks some of the light from passing through the lense (low beam). When high beams are activated the seleoid moves the flap out of the way, allowing full light to pass through the lense (high beams). Bi-Xenon came out around 2002.
There are two regulating forces to HID. In the Americas, the DOT sets rules and regulations. In europe, ECE is the governing body. I'm not positive on the differences but it's my belief that the ECE standards are more developed, better researched, and safer. Consult HIDPlanet for much more information and resources, parts, and forum help. There's also this thread which has a LOT of information in regards to HID kits.
Now, for some pics to illustrate what I'm talking about...
This is the cutoff created with a true HID Setup (xenon bulb mounted in a projector with ballast)
This is what happens when you mount a xenon bulb directly into a halogen housing (aftermarket kits, ebay, car toys, no projectors)
Notice the light has no distinct cutoff and the light spread out in all directions
These are Bi-Xenon projectors/lenses. The projector holds the bulb and focuses the light
This is how they look installed on a car from the factory
Here are the parts necessary in doing a proper retrofit to your car.
In the top center are the bulbs/projectors. Outside of them are the high voltage wires (in this case the spec is D2S). Below the projectors are the HID Xenon bulbs. The wires attach to the ballasts (at the bottom of the pic) which also include the igniters in this case.
These are also Projectors with separate igniters
First off, HID stands for High Intensity Discharge. Unlike standard halogen lighting, HID lighting typically burns a Xenon gas at such a rate faster than the human eye can detect, hence a solid beam from the lights. HID parts include a ballast, igniter, projectors/reflectors (including dish and lense), and bulb. HID setups create a very intense, very bright light, very closely simulating sunlight during the day. The projectors/lenses create a very sharp cutoff in their beam pattern; that is there is a distinct horizontal line between light and dark. This is what prevents blinding oncoming traffic from being blinded
Again, parts included in an OE setup include ballast, igniters, projectors/relfectors (depends on the spec), bulbs, high current wires, auto-levelling mechanisms, and lense washers. Wiring starts at the ballast (which powers the bulb) connects through a high current wire to the igniter. The igniter is what starts the initial power-on of the bulb (approx 23kV of power). Sometimes the igniters are built into the ballast, sometimes on the wire between the ballast and bulb, and sometimes directly to the rear of the bulb. The bulb then sits inside the projector and the projector inside a large clear plastic housing. Recently auto-levelling and lense washers have come out. Auto-levelling is when a small motor controls the up/down aim of the cut off line when there is a load in the rear of the car (weight in back of the car pushes the headlight beam up). Lense washers are mounted on the outside of the car to keep the large clear lenses clear. I'm not positive if auto-levelling or lense washers are required for legality, but I've seen cars with and without both technologies (BMWs have both, some Acuras have neither).
HID is legal. It comes on high end vehicles such as Beamers, Mercades, Audis, some Volkswagons, etc. HID is legal when the high output bulbs are paired with a proejctor/reflector. HID is ILLEGAL and UNSAFE when a high intensity bulb and ballast are fitted inside a halogen bulb housing (IE Car toys HID kits; also found on ebay). These kits are labeled as "for off road use only" as the light emitted from this setup can blind drivers. The way around this (though technically still illegal) is to take a true HID setup (such as OEM from BMW) including the bulbs, ballasts, and projectors... and then fit the projectors into the halogen housing.
The DOT recently passed a law stating that any alterations to headlights in such manner as not offered from the factory are illegal. Fitting an HID bulb into a halogen is illegal. Technically so is fitting an HID bulb and projector into a halogen housing. Police are not thoroughly and regularly enforcing the HID laws passed by DOT, therefore you could get away with either setup. The problem in using a xenon bulb in just a halogen housing is that there is no distinct cut-off line as there is with projectors. In a halogen housing, light is emitted all over the place with no definition, creating a problem in blinding oncoming traffic.
There are multiple specs and manufacturers for HID setups. Bosch, Hella and Valeo are a few mfrs, each with their own generation of parts. There are also multiple specs, H7, D1S, D2S, etc etc. Sometime specs work interchangeably, though it isn't wise to rely on parts being inter-changeable. The best and safest way to create a semi-legal/working HID setup for your non-HID car is to purchase parts from a single spec/platform and retrofit a projector into your housings.
Xenon technology, when first becoming popular in the late 90s, only provided light as a solution for low beams. Since then a technology has come out called Bi-Xenon, which provides high and low beam light from a single bulb/projector. The way this is accomplished is by taking a projector housing and mounting a small flap/selenoid near the bulb. This flap blocks some of the light from passing through the lense (low beam). When high beams are activated the seleoid moves the flap out of the way, allowing full light to pass through the lense (high beams). Bi-Xenon came out around 2002.
There are two regulating forces to HID. In the Americas, the DOT sets rules and regulations. In europe, ECE is the governing body. I'm not positive on the differences but it's my belief that the ECE standards are more developed, better researched, and safer. Consult HIDPlanet for much more information and resources, parts, and forum help. There's also this thread which has a LOT of information in regards to HID kits.
Now, for some pics to illustrate what I'm talking about...
This is the cutoff created with a true HID Setup (xenon bulb mounted in a projector with ballast)
This is what happens when you mount a xenon bulb directly into a halogen housing (aftermarket kits, ebay, car toys, no projectors)
Notice the light has no distinct cutoff and the light spread out in all directions
These are Bi-Xenon projectors/lenses. The projector holds the bulb and focuses the light
This is how they look installed on a car from the factory
Here are the parts necessary in doing a proper retrofit to your car.
In the top center are the bulbs/projectors. Outside of them are the high voltage wires (in this case the spec is D2S). Below the projectors are the HID Xenon bulbs. The wires attach to the ballasts (at the bottom of the pic) which also include the igniters in this case.
These are also Projectors with separate igniters