A ring with built-in LED chip.
Step 1: Two Identical Rings.
First I made 2 identical rings.
if you don't have access to a chuck lathe, you can buy two rings.
Check here for a chuck lathe in your city: http://hackerspaces.org/wiki/lathe
draw a recess for the 5mm LED
Step 4: Recess for the LED
for the recess, you can use a dremel and a file.
Step 5: Soldering
now, you can stuck it together with glue.
one half is the anode, the other half is the cathode.
solder the LED from inside.
now you need a second, similar ring, with a hi-cap capacitor instead of the LED.
--> if the rings touch each other, the LED is shining