I finally finished my ringlight project. I can't take photos thru my scope with my camera, but I have put up a brief webpage with a couple of pix of the light.
It uses four 1-watt Luxeon LED's with 30-degree collimators, held in a ring around the microscope objective. The diameter of the ring is about 4", but it isn't really a ring, just four lights that are each about 2" displaced from the objective axis.
Each of the lights is aimable so their beams will converge at the workplane about 6-1/2" below. They are also each individually dimmable at the control box, using thumbwheel pots. There is no color shift when dimming. Maximum brightness is almost too bright to be comfortable even at max zoom. The light in the field of view is bright, white and very uniform.
Tools in the work region (tweezers, soldering iron, solder etc) cast only faint shadows, just enough to give 3D cues. Nothing anywhere runs even warm, much less hot.
Ths is not a particularly complex project, but it's considerably more than a one weekend project. For me, it was absolutely worth it. I am going to enjoy using this tool a lot.