How lightsabers worked in 1977

The original lightsabers were powered by electric motors. Which were attached to a spinning pole that was covered in reflective material
With the correct camera angle, and with the poll spinning by the electric motor it would give the blade a flicker
This setup was very fragile and by the end of a new hope out of a dozen or so lightsabers.. only 1 motorized stunt was still working..
Production then ditched the electric motor setup for the ESB, and ROTJ but the blades were still covered in the reflect material to help the rotorscopers! ;)