I know everyone else uses super-powered LEDs with much better results, but I happened to be messing with electroluminescent wire at the time. Obviously a less-than-perfect solution, but better than a flashlight at least. I wouldn't recommend it if you're trying for the classic Star Wars look, but it's still an interesting effect. Also, thanks to the vagaries of amateur photography, the color came out wrong; they're both more green than blue.
I don't remember what exactly I used for the blade, but I think it was either 1in PETG or polycarbonate. I actually went to the distributor's will call desk to pick up the material and danced around the subject of what I was using it for. When I finally admitted it was for a light saber, the guy at the desk just laughed and said "Yeah, we get that a lot. A lot of people come here for stuff to make Stormtrooper armor, too." Although the blades themselves are relatively sturdy, their mooring to the hilts are not. I tried diffusing the light with a combination of sanding the exterior and spraying it with a frosting paint, but that obviously could've gone better.
The first I made was the black one, made smooth with a bunch of slip-fit PVC connectors and wrapped with 5mm macrame cord. The battery is kept in a separate compartment towards the pommel and can be replaced by sliding out the end plug. The light is switched by the EL wire inverter, which I screwed and taped into place towards the hand guard.
I had enough materials leftover to make another, so I went and made the silver one. I used a bunch of threaded PVC connectors, which gave it that really knobby look. I painted it with some metallic spray paint we happened to have, then painted in the recesses and such with plain ol' black acrylic. I don't remember where I got it, but I used a knurled dimmer switch to control the light and embedded it in the pommel. It was a lot trickier to wire; I had to remove a lot of the inverter's housing to get it to fit into the grip.