In SWE4, when Darth and Obi Wan are fighting, Obi points his saber to the screen, and the sides stop lighting up. It looks like a fiber optic cable. Only the top is lit.
Yeah! I found that so annoying too. But I think they used metal bars and than when the film went to the special people they added in the light, so maybe they weren't sure what to do when the lightsabre pointed at the screen.
ok im here to let you know that the light sabers are metle rods with fancy hilts or holders witch ever you want to call it the wire was proply used to make a light light up on the hilt