Adding HIDs to 06 Prius

There is a slight difference in assemblies…With the HID one, there is a High beam "lever" that moves back and forth from dim to bright when the driver moves the lever for bright/dim lights…i believe the halogen assembly does have that because the halogen bulb had 2 filaments in it, whereas the HID bulb does not. So to convert properly, you would have to have the corresponding power requirements and the assemblies …then the actual bulbs...

 

There are also going to be differences in the reflector, visible to an untrained eye or not.

 

The HID's do have a leveling system. This is nothing to do with altering the brightness neither does the dimmer switch with halogen headlamps. The leveler is worked off a sensor on the rear suspension that lowers the aim of the headlamps if a load is being carried in the rear of the car causing the normal headlamp aim to be higher and compensating for this automatically.
There are conversion kits that work well, by changing the bulbs and adding the required power supplies, but may or may not be illegal in your country/state.

John (Britprius)

 

"Illegal" has two steps in the US.

It is illegal for any vendor to offer HIDs in a vehicle not originally equipped with them. (this is why there are no big name HID kits, no one can build a sustainable business, they will be shut down by the NHTSA) If you use ALL the parts in a stock Prius with HIDs, you could sell that kit legally.
Daniel Stern Lighting Consultancy and Supply
http://isearch.nhtsa.gov/files/Shih.3.html

Second part of illegal is actually driving on US Highways. (This is why so many kits claim to be for off road use only)
That is state law and will vary by state. You do not mention what state you are in.

 

Would this also apply if say Toyota offered a retro fit kit supplying all the parts fitted to the versions of the Prius with HID's
This is not meant to be flippant, but the law seems to say that unless they were fitted at the factory there is no legal way "even using OEM parts" they can be fitted. This of course by definition rule out the fitting of projector HID's within the headlamp units.
In the UK governed by EU regulations HID's can be retro fitted or any type of light unit provided they have the relevant EC markings, and with any required additional equipment.

John (Britprius)

 

FMVSS 108 is a complex document. I read it that there are headlight assemblys A through H and each has it's own conforming bulb. You can not use a bulb from one headlight assembly in another. My understanding is that if you use ALL the original parts, then the bulb conforms to the assembly it is in and is legal. I may have missed some other spec in 108.

FMVSS No. 108 Full Text

 

Having scanned through the above text I can see on at leased four counts in the US the modification of headlamps by fitting projectors within the housings is illegal or by fitting of the wrong type of bulbs, but changing out the headlamps as far as I can tell to different ones "provided they are correctly marked by the manufacturer on the outside lens (cover)" is not. As you correctly state this is a complicated document not made any more easy by being written in legalistic gibberish.

John (Britprius)

 

You probably could trade your car and buy another Prius with HID's for less money than buying Toyota parts to do the upgrade.

 

That Daniel Stern link above does a great job of explaining why HID conversion kits are a bad idea. Converting with all the factory parts would work, but would be quite difficult I imagine.