Theory question for Ra.

[Eamon]

If this has been asked before, I apologize. If so, I couldn't find it.

There was a thread a while ago on the bicycle forum about beam shape for bicycle headlights. That thread was a followup on this one.

Is it possible to design a single optic that can be made to throw a high and low beam? A La automotive lighting?
If so, could it be done in the size range of a bicycle headlight?
I can sort of visualize where it might be doable with two or more emitters, but I know absolutely f**k all about optical theory, and imagining is all I can do.

Eamon