But I respectfully disagree to some of your technical information. The beam pattern does not come from the bulb shape; the beam pattern is directly related to the bulb housing. The bulb housing is engineered so that it will properly project or mirror the lights coming from the bulb to specific areas on the road. If you look inside the bulb housing, you'll see curvature or patterns. These curvature patterns direct lights from the bulb into the road. If you don't touch the housing adjustments, you should be fine...and yes, there will be some extraneous lights outside of the designated projected zones but that is the effect of brighter and more powerful light.
you are correct to a point. but the arc in an aftermarket HID bulb is indeed shaped differently. the arc of light is in a diffrent location than the fillament from a hallogen bulb. imagine taking a maglight flashlight and shining it waaaay down into your backyard. now, take the end of the flashlight and turn it ever so slightly to the left or the right. the beam pattern changes drastically, and you've moved the bulb less than a millimeter. that is how sensitive the reflectors are.
Originally Posted by BlackNightling
There are quite a few cars out there that have standard reflector type housings, but came with HID bulbs (ie some of the last generation Ford Mustang's, Lexus IS200, Lincoln Towncar, etc.) The point is that the light comes from a focal point and the reflector or projector pinpoint that light to a certain shape, regardless of the shape of the bulb.
correct (except for the mustang part, they use projectors. i'm a mustang guy
). but in those situations, those housings were designed to properly project the light coming from the HID bulb. by changing from a hallogen to an HID bulb, you have moved the focal point, so no amount of up or down aiming can get that focal point back to where it belonged, thus the poor beam pattern.
this is an exerpt from the site i linked. it explains what i'm trying to say and has a diagram of the differences in the light sources.
Originally Posted by Daniel Stern Lighting
A halogen bulb has a cylindrical light source: the glowing filament. The space immediately surrounding the cylinder of light is completely dark, and so the sharpest contrast between bright and dark is along the edges of the cylinder of light. The ends of the filament cylinder fade from bright to dark. An HID bulb, on the other hand, has a crescent-shaped light source -- the arc. It's crescent-shaped because as it passes through the space between the two electrodes, its heat causes it to try to rise. The space immediately surrounding the crescent of light glows in layers...the closer to the crescent of light, the brighter the glow. The ends of the arc crescent are the brightest points, and immediately beyond these points is completely dark, so the sharpest contrast between bright and dark is at the ends of the crescent of light...When designing the optics (lens and/or reflector) for a lamp, the characteristics of the light source are the driving factor around which everything else must be engineered. If you go and change the light source, you've done the equivalent of putting on somebody else's eyeglasses: You can probably make them fit on your face OK, but you won't see properly.
here are three examples from the website that i linked. it shows a government test of HID bulbs. they tested the beam pattern from a hallogen bulb. then put in an HID bulb, and even aimed it the best they could. it still failed miserably. i wish they hadn't aimed it so that you could see the effect of just swapping one for the other. by aiming it, they tainted the results IMO.
1998 Nissan Frontier
(skip to page 11 for test results)
1996 Chevrolet Lumina
(skip to page 9 for test results)
1998 Nissan Frontier (test #2)
(skip to page 12 for test results)
again, i'm not trying to tell anyone what to do, just trying to keep misinformation out of the forums. i go through this on almost every board i'm on, because the common misconception is that aftermarket HID kits are so much better than hallogens. just yesterday i had this conversation with the long distance kicker of the baltimore ravens. he had no idea about the side effects and took them out of his 2011 dodge ram.
but we're getting off topic. mods, feel free to split these posts up into another topic if needed.