I think this article might shed some light on why HIDs are being banned.
Apparently HIDs are being targetted because of the fact that because they don't have conventional filiments, the light source isn't where it was with the oem bulb they replaced.
Since HID light source is an arc that doesn't always eminate from the same place within it's capsule it interacts differently with the reflector system that was built to reflect a filimented bulb.
I guess this is why you have to sometimes re-aim your headlights when changing out burned out bulbs of the same type.
The article is from some guy named Daniel Stern who is supposably an expert in lighting glare. I can't find the actual source for this so I can't vouch for its accuracy but it makes sense to me when I read it.
It is reprinted from HIDforum.com
Article Begins:
There's a lot of handwringing going on, and there's a lot of poor-quality information getting tossed around in the wake of the announcement that the US National Highway Traffic Safety Administration (NHTSA, the agency under DOT charged with setting and enforcing auto safety standards) is cracking down on the importation and sale of HID "retrofit" kits.
First off, yes, there are problems -- some of them very large and literally glaring -- with the US vehicle lighting regulations. The minimum performance standards for headlamps are pathetic, precisely-formed beam patterns are allowed but not required, red rear turn signals are still allowed, side turn signal flashers are still not required, do-nothing "fog lamps" are allowed and unregulated, etc. This is not to say there are no shortcomings in the rest-of-world European ECE regulations -- there are, they're just different shortcomings!
But, contrary to opinion of late, the HID kit crackdown is not occurring because NHTSA's regulations are antiquated. It is not occurring because of a words-based technicality (no filament in an HID burner so HID conversions are automatically out). It is occurring because HID "conversion" kits are, quite simply, the wrong way to do it.
Undoubtedly, those fascinated by the appearance of an HID headlamp (and others) will disagree, but here are the physical facts of the matter:
These products mainly consist of an HID ballast and bulb for "retrofitting" into a halogen headlamp. Often, these products are advertised using the name of a reputable lighting company ("Real Philips kit! Real Osram kit!") to try to give the potential buyer the illusion of security. While some of the components in these kits are sometimes made by the companies mentioned, the components aren't being put to their designed or intended use. Reputable companies like Philips, Osram, Hella, etc. NEVER endorse this kind of "retrofit" usage of their products. Other "retrofits" come from companies generally known for lighting dreck and schlock -- LED-wafer-on-a-bulb-base "retrofits", cheesy little foggy lites, etc. No matter...the problem with HID retrofits isn't a build-quality constraint; it's an optical-physics constraint.
Halogen headlamps and HID headlamps require very different optics to
produce a safe and effective -- not to mention legal anywhere in the world -- beam pattern. How come? Because of the very different characteristics of the two kinds of light source.
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 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 -- they may fit on your face OK, but you won't see properly.
Now, what about those "retrofits" in which the beam cutoff still appears sharp? Don't fall into the trap of trying to judge a beam pattern solely by its cutoff! In many lamps, especially the projector types, the cutoff will remain the same regardless of what light source is behind it. Halogen bulb, HID capsule, cigarette lighter, firefly, hold it up to the sun -- whatever. That's because of the way a projector lamp works. The cutoff is simply the projected image of a piece of metal running side-to-side behind the lens. Where the optics come in is in distributing the light (under the cutoff). And, as with all other automotive lamops (and, in fact, all optical instruments), the optics are calculated based not just on where the light source is within the lamp (focal length) but also the specific photometric characteristics of the light source...which parts of it are brighter, which parts of it are darker, where the boundaries of the light source are, whether the boundaries are sharp or fuzzy, the shape of the light source, etc.
There are more "gotchyas" when pondering halogen-to-HID "retrofits". The only available arc capsules have an axial (fore and aft) arc, but many popular halogen headlamp bulbs, such as 9004, 9007, H3 and H12, use a transverse (side-to-side) and/or offset (not directly in line with the central axis of the headlamp reflector) filament, the position and orientation of which is physically impossible to match with a "retrofit" HID capsule. Just because your headlamp might use an axial-filament bulb, though, doesn't mean you've jumped the hurdles -- the laws of optical physics don't bend even for the cleverest marketing department, nor for the catchiest HID "retrofit" kit box.
The latest gimmick is HID arc capsules set in an electromagnetic base so that they shift up and down or back and forth. These are being marketed as "dual beam" kits that claim to address the loss of high beam with fixed-base "retrofits" in place of dual-filament halogen bulbs. What you wind up with is two poorly-formed beams, at best. The reason the original equipment market has not adopted the movable-capsule designs they've been playing with since the mid 1990s is because of the near-impossibility of controlling the arc position accurately so it winds up in the same position each and every time. There are single-capsule dual-beam systems appearing ("BiXenon", etc.), but these all rely on a movable optical shield, or movable reflector -- the arc capsule always stays in one place.
The OE engineers have a great deal more money and resources at their
disposal than the retrofit guys -- if a movable capsule were a practical way to do the job, they'd do it. The "retrofit" kits *certainly* don't address this problem anywhere near satisfaction. And even if they did, remember: Whether a fixed or moving-capsule "retrofit" is contemplated, solving the arc-position problem and calling it good is like going to a hospital with two broken ribs, a sprained ankle and a crushed toe and having the nurse say "Well, you're free to go home now, we've put your ankle in a sling!" Focal length (arc/filament positioning) is ONE issue out of several.
The most dangerous part of the attempt to "retrofit" Xenon headlamps is that sometimes you get a deceptive and illusory "improvement" in the performance of the headlamp. The performance of the headlamp is perceived to be "better" because of the much higher level of foreground lighting (on the road immediately in front of the car). However, examining isoscans of the beam patterns produced by this kind of "conversion" reveals *less* distance light, and often an alarming relative minimum where there's meant to be a relative maximum in light intensity. When you *think* you can see better than you can, you're *not* safe.
It's tricky to judge headlamp beam performance without a lot of knowledge, a lot of training and a lot of special equipment, because subjective perceptions are very misleading. Having a lot of strong light in the foreground, that is on the road close to the car and out to the sides, is very comforting and reliably produces a strong *impression* of "good headlights". The problem is that not only is foreground lighting of decidedly secondary importance when travelling much above 30 mph, but having a very strong pool of light close to the car causes your pupils to close down, *worsening* your distance vision...all the while giving you this false sense of security. This is to say nothing of the massive amounts of glare to other road users and backdazzle to you, the driver, that results from these "retrofits".
HID headlamps also require careful weatherproofing and electrical
shielding because of the high voltages involved. These unsafe "retrofits" make it physically possible to insert an HID bulb where a halogen bulb belongs, but this practice is illegal and dangerous, regardless of claims by these marketers that their systems are "beam pattern corrected" or the fraudulent use of established brand names to try to trick you into thinking the product is legitimate. In order to work correctly and safely, HID headlamps must be designed from the start as HID headlamps.
The only safe and legitimate HID retrofit is one that replaces the
*entire* headlamp -- that is lens, reflector, bulb...the WHOLE shemozzle-- with optics designed for HID usage. On models for which no complete HID headlamps exist, it IS possible to get clever with
the growing number of available products, such as Hella's modular
projectors available in HID or halogen, and fabricate your own brackets and bezels, or to modify an original-equipment halogen headlamp housing to contain optical "guts" designed for HID usage. But just putting an HID bulb where a halogen one belongs is bad news all around.
And *that*, folks, is why HID kits are getting targetted for enforcement.
DS"
