I believe as long as all the optics are DOT, it's legal, at least in the United States. That's why crazyjoker77 mentioned the option of reusing the projectors from a car that had HID's. I'm pretty sure the headlight cover doesn't count since it's only there to protect the optics.
RE read ezarcs post
Yeah, there seems to be a lot of confusion about what’s legal where. I found this thread at CPF by Scheinwerfermann has links to a lot of the local laws. Helped clear that up for me. I’ve settled on these Philips X-treme Vision for now. Thanks!
A fixed cutoff is easy to do. Even bixenon retrofit kits come with a movable shutter, so they'll definitely come with a HID projector conversion. That's why the projector is retrofitted. Older cars didn't have leveling, so that shouldn't be a legal problem, but even that may be retrofittable someday if it isn't already. Again, that's for the United States.
I think the intent of the law is more important than the letter of the law. Make a light look like it could have come from the factory in every way, and it's highly unlikely that you'll get in trouble for them. And why should you?
If I do a retrofit, I'll buy a full conversion kit from these guys.
The intent is more important, but if they can use the letter to throw the book at you then they will, so keep that in mind
It's always possible. I try to keep and store the original unmodified part that way I can easily fix it if I get a ticket. Fix it tickets usually have a very small fine. If there's no other illegal mods, the book thrown will be very thin.
Fortunately there's enough people out there with poorly adjusted HID kits that someone with a well adjusted good kit attracts virtually no attention. Those guys made it possible for me to get away with using 100 watt halogen bulbs for years.
An XML running at 10 watts will output 1000 lumens. And the heatsinking required for 10 watts is not that massive. An SRK body or CPU heatsink can easily maintain that light level and only runs 30C above ambient. LEDs can very easily do the job… it’s the required optics that are not so easy for the DIY’er.
So why does my flashlight get to over 60ºC?
i agree it can be done, but i would expect a failsafe such as tiny fan or something
There's still the problem of making sure that heat sink is cooled. It doesn't do much good if it's a part of the car that gets minimal air flow. Another problem is that the ambient temperature in an engine bay is already pretty high, and even if it's separated well, there are plenty of places where the headlights will be expected to perform when it's well above 110°F outside.
That's why I want to see the Corolla headlight. It's budget car, but it appears to use a single LED for the headlight. This headlight has to be dead nuts reliable under all conditions or it wouldn't be in a Corolla, so I'm very interested how they handled cooling simply enough to justify installing it in an econocar.
perhaps its replaceable and rated for 1000 hours 
Replaceable takes on a different meaning to a community of modders. :D
There ARE 100% LED headlight combining dip and main in the UK, but they have not as yet(yesterday) been submitted for approval, they have existed for around 4 years FULLY working, and used at night for hundreds/thousands of miles, I know this as the guy who built up the light looms is the same guy who did my motorsport loom on my sierra cossie, that helped me just eat a Aston Martin DB9 yesterday ha ha, bet he was pissed with my 25 year old 4 pot eating his car.
I think before the end of the year they will be available certainly from some small volume sports car makers in the uk, whose biggest market is the USA.
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