I was chatting to bro the other day about why is it most cars only have dipped beam as HIDs (the sorts of cars he is a designer for have full beam HIDs as well) - its to do with heat disipation both off the lenses (which I couldn't understand as they use less power :-/) and the ballast packs.
Lol, not an elecronic eng is he......
The reality is that the life of a HID is not so much time limited but cycle limited i.e. they only give a certain number of on/offs.
And as you can imagine, supporting full beam results in a lot of cycles.
Hence why on some cars they use a solenoid shutter on the dip beams to support full beam using HID's on the same bulb.
The bubs themselves run at MUCH lower temperature so cant see heat being an issue.
LOL, no, he's definately not.
He did say something about they have to run all the time, as HIDs have a 0.75s turn-on time (hence no good for full beam), using shutters as you say (in addition to a seperate dipped HID on the last design they did).
He did say that cooling the lights was a challenge - mind you, a bloody great 5.5l supercharged lump producing 600+ bhp under the bonnet isn't going to keep anything cool

- prototype testing proved the headlights were overheating.