I replaced my main bulbs with hid xenon in my 98 range rover hse

HID headlights are one of the best modifications you can make to a car. When they first came out, they were very expensive, but now the costs are extremely reasonable ($60-80 including shipping from a variety of sources online, somewhat higher if your car has one bulb that gives both low and high beams). The light output is about 3 1/2 times the intensity of halogen headlights, the bulbs have a lifespan to rival the car itself, and yet they draw less power than a standard halogen bulb (35w vs the 55w of a typical halogen bulb).

First off, how does it work? The system includes a pair of bulbs and a pair of power ballasts to drive them. Unlike a halogen bulb, which is a glass globe with a physical filament in it (which heats up to glowing when current passes through), an HID bulb has no filament. It functions much the same as an arc welder. At either end of a glass tube with a globe in the center, is an electrode. The center globe is filled with a combination of elements, among which is xenon gas. The power ballast is basically a transformer, which takes the 12 volt input from your car and boosts it tremendously. Xenon gas lights need an initial surge of over 22,000 volts to ignite, and a steady 75-85 volts to stay lit. The transformer in the power ballast steps up your 12 volt car voltage to these levels to drive the lights. However, the current is very, very low, and the result is a power draw of only 35 watts, a lot lower than the power draw of halogen lights. When the ballast fires that initial starting voltage, the electricity arcs between the electrodes in the bulb, through the xenon globe, molecularly exciting the xenon gas and causing it to emit light.

Some cars require an additional relay harness that connects directly to the battery to turn the lights on, but most do not. Your vendor should be able to tell you if your car will need this additional harness.

There are a few things to know before you order. First, you need to know what type of bulb your car has. Remove a headlight bulb and look for the number stamped on the base of the bulb. Many Japanese and GM cars use 9006-style bulbs for low beams. German cars like Audi and VW often use an H7 bulb. You'll need to know this for your car, so you can order your HID bulbs properly.

Next, you'll need the color temperature. The temperature, or "warmth", of the light is described in degrees Kelvin. Any manufacturer that offers HID lights as standard or optional equipment, puts out kits with a color temperature of 4300K (4300 degrees Kelvin). Again, this is a measurement of color, NOT of physical temperature. They offer 4300K bulbs because natural sunlight/daylight is very close to that color, and from behind the wheel, the combination of light color and light intensity rivals that of daylight. It's also a color that is easy on the eyes, and long night drives are more relaxing than with the yellowed halogen light - I've found that I feel less fatigued with HID lights than with halogens.

With color temperature, the higher the number, the more blue the light gets. The lower the number, the more it trends to yellow (a 3000K HID kit in your foglights would be a blazing yellow/amber color, great for cutting through rain, driving snow, or fog). 4300K light is very crystalline white on the road. Moving upward through 5000K and 6000K kits, you'll get a richer white with tinges of blue. I have had 4300K and 5000K in past cars, and currently have 6000K HIDs in my Audi. I like the 6000K best, but that's personal preference, although it does seem to have the fullest light.

Going beyond 6000K, you start getting into a seriously blue spectrum, and this is not recommended - sure it looks cool, but blue is one of the worst colors for visual definition, and does not penetrate distance nearly as well as the whiter colors of the spectrum. Going to 10,000K and above makes the light almost purple - again, cool for looks, but lousy for driving.

That's about all there is to know, other than the fact that HIDs will give your car a great look, and will blow you away with the visibility improvement. I've been modifying cars for a long time, and consistently, HIDs have been one of the best functional and aesthetic improvements I've made to any of them. And if your eyesight is somewhat compromised, or you drive a lot of unlit back roads, they're going to seem like an answer from heaven for your driving:)