The HID headlights installed in cars are for the low-beam application.
These wide angle lights aren't very suitable for landing lights unless
you install them in a different, narrow beam reflector. Off road HID
lights work better as landing lights. I suppose your could rig up
something suitable out of a set of off road light housings and the guts
from a set of junkyard HID lamps.

I admit that I've wondered about high and low beam. The ones I've seen on
the road appear to cover both the high and low beam applications, but I have
no idea how they do it.

Peter