I needed to make a light saber to take it to the Light Saber Battle in San Francisco and had about a night to make one. The following really worked out for me since it didn't need any tools and all I had to do was assemble two parts -- a PVC pipe and a flashlight. The outcome was a really durable and bright light saber.
It is made with PVC pipes from Home Depot and a flashlight that fits in it. Following steps detail my experience. If you experiment with other pipes/ flashlights, please do leave a note.
Step 1: Parts
I bought the 3/4-inch red and blue PVC pipes and had the Home Depot associate cut the 5' pipe into two. If you need longer or shorter, you can specify the desired length.
Next, I bought pen flashlights as shown. They have a diameter of 0.61" and are easy to fit in the pipe. If you are experimenting with other pipes and flashlights, you may want to pay attention to the fitment of flashlight in the pipe.
The PVC pipe costed about $3.5 per 5' and the flashlights were ~$4.5 per 2-pack.
Step 2: Assembling
Put the flashlight in the pipe. In my case, the the flashlight fit the pipe snuggly. I used some tape as a good measure.
Step 3: Almost Done
Cut a small piece paper to cover the other end of the "light saber". The flashlight I used is really bright and it was annoying when the "light saber" is pointed at somebody. A little piece of paper helps soften the light.
And you are done.