Thanks audioguru, that's the type of info I have been dealing with for the last couple of years. I have been to many meetings with government officials and engineers in hopes of getting some of these lamps approved for use as replacements for incandescent lamps in the work I do. LED technology is great in so many ways, and is finally becoming mainstream.
It drives me nuts when I see those clear lamp covers with lame little LED lamps on modified cars. That and people who put tinted covers over their tail lights. These lights are critical safety devices that have been carefully engineered for everyones benifit.
I install lighting on emergency vehicles, and trust me, when you are on the side of a highway at night in the rain, you want your vehicle to look like the mothership from Close Encounters, or things get ugly really fast.
Integraoligist, replacing lamps with LED's is very complicated, and not only risks getting a ticket for having non-standard lighting, it can be a safety hazard if not done correctly.
I have seen very few aftermarket replacement lamp assemblies for passenger vehicles where the manufacturer will have a DOT or FMVSS approval certificate. The ones that do are usually atleast twice the price of a factory replacement of the incandescent type. Vehicles that use the round US40, PAR36, hotdog US60, or similar lamps as found in trucks are a different story. Nearly all of these lamps have direct LED replacements that are legal, and due to the volume, very reasonable in price.
Other than the truck type direct replacement lamps, most of the other "arrays" used in passenger vehicles ( including factory OEM ) use a PWM controller to drive many surface mount chip LED's at very high levels with controlled pulse rates to produce high output. This is not easy to do, requires considerable engineering and cost. This is why generally these LED taillights are only standard equipment on the more high-end vehicles.
While I think doing a conversion of tail lights is fine for a non-road show car, I just don't think it is feasable for the average person to attempt, given the risks involved.
/ "rant" over, I will step down from the soapbox