well well i think u've asked the right person for this question.

There are a few type of blubs out on the market these days and it makes it a bit harder for people who dont know whats what.

For starters, Normal lights we'll refer to them as Haloges, and HID's as HID's.

The main and noticable difference between Halogens and HID's is the Glow that the light gives. Ever notice when driving you see that car driving on the other side has a much brighter, Whiter and most commonly appears like they've got their highbeams on? Well Thats HID's. HID's stands for High Intesity Discharge.

The light that is dischared from a Halogen bulb is much more yellower than HID's. Yeah sure you can get like blue and white blubs, But they are only tinted glass. The Fillament is still halogen. How light is emmited from halogen blubs is by passing a electricity through a thin wire (Tungsten) and by doing this, the wire gives resistance and hence glows and gives off heat. This is where HID's differ, HID's dont use a wire but uses a gas (xenon). The electricity moves past the two electrodes and excites the gases, which in turn gives off light. However, in order to excite the gas, a higher voltage is required which is why you need a ballast to use HID's. Ballast creates high voltage (2400V Im pretty sure) and then passes that through the gas. HID's gives off a more Bluer/whiter glow on the road. The colour of the light is measured by Kelvins or K. The lower the number (ie4300K) the more yellow its going to be the more higher (ie 8000K) the more bluer/purple the light is. But when using HID's you must select the right range of lighting for best preformance, generaly this is 4300K - 6000K any more than that your losing your visablity at night.

Another thing to note, is that HID's are NOT ADR aproved, unless you have Headlight washers, and an auto leveling system. In other words Unless you got them OEM with your car, then they are illegal!

I hope that helps you.