This instructable shows how to make a ring with a glowing LED (in case you can't afford the old fashioned dull rocks).
The led is powered by two #10 hearing aid batteries. Design and print files for the 3D ring and LED holder are available at:
Print the ring and the ring cap.
Place wire wrap wire around the anode (plus end) of the LED. Place it as close to the body as possible. Cut off all of the lead that is not being used by the wrapped wire. Place heat shrink tubing over the wrapped connection and heat the tubing.
Place the LED in the cap and cut off the cathode lead where it just extends slightly beyond the cap.
Strip the end of the wire wrap wire and bend it so that it runs across the bottom of the hole in the ring. Place the wire wrap wire in the channel. Insert the batteries, positive end down in the ring.
Be certain that the LED is illuminated, then glue the two halves of the ring together with superglue.