As I remember, hamsters are nocturnal so useful for powering lights. 
Sorry, couldn't resist it.
Lol......guess inside were all jokers......
I got a cheap bag of assorted LEDs from Maplin. They were carefully selected to be the world's dimmest LEDs. I also had a Streamlight TwinTask that I'd just found out the hard way couldn't use RCR123s and was awaiting a new bulb from Lighthound. So the hole seemed to be around the right size for the leads on a 3mm LED from this bag of the World's Dimmest LEDs. So here's the pic.
Not the power LED on the old Compaq which served as my living room box (It was almost completely silent). It was actually brighter! Runtime on a dead CR123 was till I got bored and tossed the cell and the LED