It's built around a magnifier designed as an upscale version of an optical loupe. The magnifier has a clear plastic skirt that is intended to admit light from the sides. I have a small loupe made on the same principal, and it works OK. But I found that with the bigger version, the magnifier casts a shadow on the subject, and not enough light makes it in from the sides. I decided to add some LEDs for better illumination.
In order to make it as bright as possible, and to make construction neat and easy, I used a ring-shaped LED array which is marketed for use as an accent light on automobiles. It's a circuit board 80mm in diameter (just right to fit the magnifier) with 24 surface mount LEDs on one side and current limiting resistors on the other side.
I considered battery-powered options, but I wanted this magnifier mainly for use on my workbench, so I decided to trade off portability for brightness, and made it operate on 110V AC. I used a 3D printer to make a little box on the side to hold the on/off switch and contain the wiring.
I made it at TechShop. http://www.techshop.ws