88GMCtruck
I'm all 8-Luggy!
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I've dealt with and researched HIDs and housings quite a bit, so i'll throw what I know in the mix. As the owner of full HID lighting in both my trucks, I'd like to point out a few things in regards to HID lights.
Halogen bulbs utilize a filament in the bulb, and the filament can be side to side, fore and aft, or up and down depending on the bulb type. The filament is located a specific distance from the reflector of the light. This is the Focal Point. The housings are designed for this filament.
HIDs on the other hand, are almost always mounted fore and aft on the horizontal plane, and light output is actually an electrical arc (thus bending up in the middle) whereas a filament is flat. Even if the focal point is located the same distance from the housing, it in many cases is oriented differently from it's halogen counterpart thus changing the focal point of the light and creating output where it's not wanted.
DOT spec headlights are simply junk. Their system for light output is garbage in multiple respects and simply relays on being able to light up signs at a certain distance. In most cases of DOT spec lighting, there is just a wash of light over the road. This is not the case with E-code lighting. E-code lights, while illegal in the US, have mighty higher standards. E-code lights are designed with a definite cut off line, and a 15* kick up on the side to illuminate signs and pedestrians. The strict regulations of E-code lighting actually prevent glare to oncoming drivers, and put the light on the road where it is needed. This is why so many vehicles, even ones with stock halogen lighting, are blinding at night.
The best halogen conversion candidates are the H4, H7 and 9005/9006 bulbs. They are the closest matched focal point you can basically get. As far as headlights, halogen projectors are best (not cheap aftermarket crap, but OEM like Denalis). Other styles of lights can vary greatly. E-code refractor based headlights (cut lens) generally play well with HIDs as they typically incorporate a glare shield which creates a cut-off line. The glare shield cuts the stray light down considerably and focuses the light through the cut lens where appropriate. Reflector based headlights (clear lens, cut reflector) that incorporate a glare shield to direct the light properly work well. DOT refractor based headlights (cut lens) are generally less favorable as the lens itself focuses the light. Even in halogen based lights, the lens focusing the light takes any stray light inside the headlight and directs it places it may not be wanted. Overall, the focal point is the most crucial to the lights output than other instances. Overall, lights without a glare shield are a bad idea unless the lights have very good optics and the focal point is extremely accurate.
For a GMT400, cut lens stock lights are going to throw quite a bit of glare at oncoming drivers. Notice how they sucked when they were halogen? That horribly pattern isn't going to get better (just brighter) by installing HIDs. Adjusting your headlights down simply isn't going to be enough to overcome this.
Many people don't understand the difference between kelvins and lumens. Kelvins are the color of the bulb, and lumens are the actual measure of how bright the bulbs are. Generally speaking, all the lights have comparable lumen readings. Generally, the higher kelvin (color) you go the less useable light you will have. This is because our eyes see the broad range of color better than a single color, so a lower kelvin with a wider spectrum of colors appears brighter to our eyes, and thus more useable. The actual most useable output in HID lights is going to be in the 4,000-5,000 kelvin range, which is a very crisp white.
Now, it is entirely possible to install HIDs into halogen housings and not have any offensive glare. It can require some extensive work and research to get things right, but with the proper steps it is possible. I currently have shielded H4 HIDs in Bosch E-code housings for the lows and custom H3 shielded/modified reflector KC LX2 fog lights in my 88 Sierra. While the lights are much brighter than stock, the combination of the proper focal length H4 HID, bulb shielding, and E-code housing, I have non-projector lights with a definite cut-off line that don't cause offensive glare. I have never been flashed running the lows and fogs, and I've driven behind a few of my own friends, had them drive my truck behind me. The lights are honestly not offensive, and personally I think they are even less offensive than the DOT sealed beam junk it had before. If you'd like to see how I accomplished this in my truck, here is the build thread. http://www.gmt400.com/forum/showthread.php?948-88GMCtruck-s-non-projector-HID-conversion
While both my HID lights and my E-code housings are illegal, I'd be dam shocked to ever get pulled over for them.
Halogen bulbs utilize a filament in the bulb, and the filament can be side to side, fore and aft, or up and down depending on the bulb type. The filament is located a specific distance from the reflector of the light. This is the Focal Point. The housings are designed for this filament.
HIDs on the other hand, are almost always mounted fore and aft on the horizontal plane, and light output is actually an electrical arc (thus bending up in the middle) whereas a filament is flat. Even if the focal point is located the same distance from the housing, it in many cases is oriented differently from it's halogen counterpart thus changing the focal point of the light and creating output where it's not wanted.
DOT spec headlights are simply junk. Their system for light output is garbage in multiple respects and simply relays on being able to light up signs at a certain distance. In most cases of DOT spec lighting, there is just a wash of light over the road. This is not the case with E-code lighting. E-code lights, while illegal in the US, have mighty higher standards. E-code lights are designed with a definite cut off line, and a 15* kick up on the side to illuminate signs and pedestrians. The strict regulations of E-code lighting actually prevent glare to oncoming drivers, and put the light on the road where it is needed. This is why so many vehicles, even ones with stock halogen lighting, are blinding at night.
The best halogen conversion candidates are the H4, H7 and 9005/9006 bulbs. They are the closest matched focal point you can basically get. As far as headlights, halogen projectors are best (not cheap aftermarket crap, but OEM like Denalis). Other styles of lights can vary greatly. E-code refractor based headlights (cut lens) generally play well with HIDs as they typically incorporate a glare shield which creates a cut-off line. The glare shield cuts the stray light down considerably and focuses the light through the cut lens where appropriate. Reflector based headlights (clear lens, cut reflector) that incorporate a glare shield to direct the light properly work well. DOT refractor based headlights (cut lens) are generally less favorable as the lens itself focuses the light. Even in halogen based lights, the lens focusing the light takes any stray light inside the headlight and directs it places it may not be wanted. Overall, the focal point is the most crucial to the lights output than other instances. Overall, lights without a glare shield are a bad idea unless the lights have very good optics and the focal point is extremely accurate.
For a GMT400, cut lens stock lights are going to throw quite a bit of glare at oncoming drivers. Notice how they sucked when they were halogen? That horribly pattern isn't going to get better (just brighter) by installing HIDs. Adjusting your headlights down simply isn't going to be enough to overcome this.
Many people don't understand the difference between kelvins and lumens. Kelvins are the color of the bulb, and lumens are the actual measure of how bright the bulbs are. Generally speaking, all the lights have comparable lumen readings. Generally, the higher kelvin (color) you go the less useable light you will have. This is because our eyes see the broad range of color better than a single color, so a lower kelvin with a wider spectrum of colors appears brighter to our eyes, and thus more useable. The actual most useable output in HID lights is going to be in the 4,000-5,000 kelvin range, which is a very crisp white.
Now, it is entirely possible to install HIDs into halogen housings and not have any offensive glare. It can require some extensive work and research to get things right, but with the proper steps it is possible. I currently have shielded H4 HIDs in Bosch E-code housings for the lows and custom H3 shielded/modified reflector KC LX2 fog lights in my 88 Sierra. While the lights are much brighter than stock, the combination of the proper focal length H4 HID, bulb shielding, and E-code housing, I have non-projector lights with a definite cut-off line that don't cause offensive glare. I have never been flashed running the lows and fogs, and I've driven behind a few of my own friends, had them drive my truck behind me. The lights are honestly not offensive, and personally I think they are even less offensive than the DOT sealed beam junk it had before. If you'd like to see how I accomplished this in my truck, here is the build thread. http://www.gmt400.com/forum/showthread.php?948-88GMCtruck-s-non-projector-HID-conversion
While both my HID lights and my E-code housings are illegal, I'd be dam shocked to ever get pulled over for them.