Here we go...
It's HIGHLY illegal, so much so that it's Federally Prohibited
. The very reason newer vehicles are allowed to use HID lamps is because of an advanced Auto Leveling system that PREVENTS the driver from blinding oncoming traffic, regardless of whether or not he or she decides they want to use the high beams. If the vehicles sensors sense light shining at it, it will automatically flick the high beams off.
Not only that but it also automatically levels the projectors each time you start the vehicle up, so that they are aimed absolutely perfectly. These headlamps are 100% in compliance with Federal DOT AND European lighting codes- the 2 most strict lighting codes there are out there. That is why manufacturers can use HID lamps, because they specifically designed the vehicles headlamps for them.
You can legally buy them all you want. Doesn't make them legal for on road use. You can put red brake lamps on the front of your vehicle, and not wear seatbelts either. Doesn't make it legal to do either. Infact, if you read the box, usually they will clearly state "For offroad use only." right on the side. If it's imported directly from China then it will not state this, the Chinese don't care either way, and are under no such obligations to warn you about their products.
The very reason why they have been banned from road use is because the headlamps on your vehicle are designed around a VERY specific bulb, typically a 9003 bulb (or an H4 as it's also known). This bulb has a specific length to it, features 2 filaments (one directed towards the top of the headlamp for low beams, one non directed for high beams), and radiates light out in a circular pattern. This circular pattern of light is mainly what the reflector OR fluted lens is designed around- it shines the light into the 'Playing Field' to give you the light you see on the road. The lens or reflector is ALSO designed to refract a small portion of light upward and towards the passenger side of the vehicle to illuminate road signs that may be overhead and off to the sides of the road. There is almost no light reflected upwards on the drivers side of the vehicle.
On the other hand, an HID lamp creates light by using nearly 25,000 volts of electricity to ignite a small amount of sand inside of the lamp. This in turn creates a plasma arch of light. The light radiating off of an HID lamp is in an arch shape, not a circular shape like a Halogen lamp. Ontop of this, the HID bulb is longer. So not only do you have a different source of light, but you also have the light coming from a different location.
When this arch of light hits the reflector at a different angle, it scatters the light forward and out, rather than into the playing field. It's similar to driving with your high beams on all the time
. The biggest side effect is that you actually get LESS usable light into your playing field, because it's not being refracted properly. Lighting up reflectors for miles is not lighting up the road. The small bits of light that are being scattered everywhere light the reflectors up because of that exact reason- light is going everywhere. If the cutoff line was proper and in compliance to DOT lighting code, then it wouldn't illuminate road reflectors beyond what you can see.
A proper Projector retrofit refracts ALL of the light into the playing field, rather than into the eyes of oncoming drivers. Usually they come in a 'Bi-Xenon' variety which gives you a high and low beam. The cutoff is razor sharp as well. Here is a photo featuring the illegally retrofitted HID lamps on top, and a proper Projector retrofit on bottom:
You can see all of the scattered light in the top image along with the piss poor cutoff line, and the bottom image shows you what a proper Projector retrofit looks like. Almost no light is scattered above the cutoff line, aside from a very tiny bit which is used to illuminate overhead road signs.
This photo shows you what a cutoff line looks like from a factory Halogen lamp setup:
DOT code dictates that a soft cutoff line be present, so that is why it is not razor sharp.
Another thing is your factory Halogen headlamps will put out more usable light than an improper HID retrofit. Your eyes will thank you, especially after a long drive. If your headlamps are dull, that means that a few things could be at play here. One is that your factory OE bulbs could be worn out- after about 5-6 years, they will appear to be less bright, especially if you drive with your headlamps on all the time. The filament physically burns out. Secondly, your lenses could be oxidized, which is a common issue with plastic lenses. A simple headlight restoration kit can fix your issue in an hour or two. Lastly, your plugs could be corroded, but typically auto makers insulate them and protect them with grease so that this will not happen. Doesn't hurt to check.
(our YJ's in particular feature a piss poor wiring job from the factory, which further reduces light output- search the forums for the ever so popular 'Headlight Relay Upgrade' which significantly boosts light output, even with the stock Wagner lamps)
On the subject of Kelvin (or color temperature), any color outside of white light is absolutely illegal for road illumination use. Halogen lamps emit white light, despite it having the appearance of a yellow-ish tint. A 4500K HID bulb is just about pure white. A 10,000K bulb is pure blue, and a 3000K bulb is pure yellow. Anything above 6000K or below 4000K begins to emit less and less light, and merely changes the output color (most people are under the assumption that the higher the Kelvin of the bulb, the more light output there is- this is 100% false. Kelvin merely refers to the color temperature
, referring to the actual output color). Your eyes will feel like they are on fire after seeing a pure blue or yellow light for so long.
Now that you're edumacated, hopefully you will make the right choice and remove the pathetic headlamps you've installed, and realize the mistake you have made. Hopefully you will wish to take the right steps to either install a proper sealed beam conversion with H4 Halogen bulbs, or retrofit a proper Projector setup.
If anybody has any more questions, feel free to ask. My area of expertise is artificial lighting, so I'm quite educated on it.
Oh, and if you are sporting an illegal HID retrofit, be prepared to see just what 200 watts of pure Halogen light looks like. A lot of people around here don't like it, but they should have thought about that before they broke the law