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High Intensity Discharge FAQ

What are HID's?

The best way to describe an HID headlight is to compare it to a more conventional halogen headlight. A halogen bulb consists of a wire filament surrounded by an inert gas. When electrical current is applied to the filament, it glows brightly to produce light. Contrast that with an HID bulb which has no filament, but instead consists of xenon gas, mercury, and metal halide salts. The xenon gas is ignited by an arc of high-voltage current (in the region of 23kV) and the burn is sustained by a constant voltage which is supplied by a ballast.

A standard filament bulb requires a lot of energy to produce light (55W/60W) a HID burner does not require the same, HID ballast in kits come in 35W and 55W formats, as HID's use there power more efficiently 35W is more than enough for on-road use. Most kits sold as 55W dont come anywhere near that rating and have a short lifespan.

HID "look" bulbs will not give you the same type of light as true HID's, many use fancy gases/glass tints to produce a better quality light, some are just a higher wattage bulb, which can cause damage to the vehicles wiring and the lamp housing itself.

What is meant by color temperature?

K (Kelvin) is used when referring to HID's as a way to describe the color temperature of the light output. 4300K is the brightest, most natural white light similar to that of daytime sunlight, and therefore the HID color temperature used most in the OEM automotive industry. When you look at the light coming directly out of an HID headlight, it possesses a bit of a blue or purple hue which most people recognize as the expensive, elegant look characteristic of HID's. For this reason, some HID kit manufacturers produce 5400K, 6500K, 8000K, etc. bulbs that give an even more distinct blue hue but at the expense of overall light output.

For comparison, most halogen headlights have a color temperature around 2200K which gives them a "dingy" yellowish appearance compared to HID's.

Common Colours:

3000K = Golden Yellow

4300K = Brilliant White (True OEM) - Brightest

6000K = White with slight blue tint (OEM look)

8000K = White with obvious Blue Tint

10000K = Blue - Dimmest


Blue light is more fatiguing to the eyes, both to oncoming traffic and to the driver. The bluer the tint cast on the road and surrounding area, the more quickly your eyes become tired. Some some install HID's mostly for the look. Be aware that most of the 6500K and higher bulbs are produced by inferior manufacturers to capitalize on the marketability of "the bigger number must be better". While most people fit 6500K and higher for the "look" you might be attracting the wrong sort of attention.

What is included with a HID conversion kit?

A typical HID conversion kit includes:

Two bulbs

Two ballasts

H4 Bi-Xenon Conversion kits contain a controller harness to retain the original Hi/Lo function

The ballasts are small boxes (one per bulb) that convert the car's 12VDC into high voltage AC required to illuminate the xenon gas. Usually built into the ballast is the igniter initially required to start the bulb. Some kits allow you to plug directly into your exiting car wiring with a minimum of splicing wires, they use the 12V from the original bulb circuits to power the ballasts. H4 kits use a different harness type, which in most cases take their feed directly from the battery and use a controller (relay) to switch the ballasts on/off and control the Dip/Main function of the bulbs.

Bulb Type:

There is almost a HID bulb to replace every standard bulb (have yet to see a H2 one (bulbs the mk2f grills use))

Most HID conversion bulbs resemble this one (except H4 & H7r):




These bulbs are specifically designed for use in reflector type lamps found on new cars, the small shield alters the beam enough to cut down on the beam scattering.

H4 Bi-Xenon (H4-3) conversion ones mostly look like this:


This bulb type uses a shield with a cutout and an electromagnet to move the bulb between the Hi and Lo Positions

NOTE:There are another type of H4 bulb which use a HID for the low beam and a Halogen for the high beam, but due to the offset of the high bulb the beam is often scattered and un-focused, the HID bulb is also a problem as the reflector is normally tow small to be of any use, causing beam scatter and dazzling on-coming drivers. (If your H4 bulb looks like the other type and doesn't have a big reflector then you will be on the equivalent of high beam all the time)

Beam Patterns:

This is how your beam pattern should look against a flat surface regardless of using standard or a conversion kit:


Note:Modern Lamp housings have a step instead of an arc but the principle is the same.

After fitting a conversion kit the beam pattern should look exactly like the standard bulbs, there should be a clear and defined cut-off and edges with little to no scatter or obvious "hotspots" (area of beam pattern with a patch of intense light) Due to the slight difference's in the position of the light source compared to a standard bulb the light might need vertical adjustment downwards to prevent dazzling on-coming drivers.

If you can not see clear cut-off's, re-check the bulb is fitted properly in the holder, if your unable to "focus" the bulb then please do everyone a favor and remove the kit from your vehicle.

Note: Not all vehicle lamp housings are suitable for HID conversions (examples being those found on mk2 Saxo's, Mk5-7 Ford Fiesta's, Honda Civics to name a few) as the scatter and hotspots can be dangerous to you and other road users. The worse lamp housing from personal experience is the Mk2 Saxo they use H4 bulbs, when fitted with HID's there is no defined "beam", just a field/puddle of light which is dazzling to all on-coming vehicles, as the driver you have no useful light output whatsoever, making it dangerous for yourself.

This thread is not to discuss the legality of HID's but to educate those that would like to fit them in the hope they will fit them properly. Its is your responsibility to make sure your conversions are fitted properly and do not blind oncoming drivers or attract unwanted attention to your vehicle

If anyone has anything they would like to see added or something I've missed then PM me.

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Hopfully this will stop all the hid threads thoughout the week

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Hate to bump an old topic, but there's a point I'd like to address:

Blue light is more fatiguing to the eyes, both to oncoming traffic and to the driver. The bluer the tint cast on the road and surrounding area, the more quickly your eyes become tired.

But my research suggests the exact opposite: that blue light actually reduces fatigue. As much as I hate to source the Daily Mail, it was the first article I came across:


And them aside, a quick Google search seems to support:


Just thought I'd throw that out there :|

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