This is a mixture of Ryan Wieber's After Effects and Photoshop rotoscoping tutorials.

1. Get your saber picture.
2. Open in Photoshop
3.Create a new layer. Make sure it's "screen" and filled with screen-neutral color. If you have more than one saber, make two layers.
4.Make sure your saber layer is selected. Using the pen tool click the bottom points of your blade. Then make a bunch of dots on the top to make it rounded.
5. Press CTRL+E to merge shape 1 with layer 1.
6. In the "filter" menu, open the "blur" submenu and give it a gaussian blur of 1.
7. Duplicate layer one 3 times.
8. Give layer 1 copy a gaussian blur of 10.
9. Give layer 1 copy 2 a gaussian blur of 20.
10. Give layer 1 copy 3 a guassian blur of 30.
11. Merge all of them to Layer 1, and NOT BACKGROUND!
12. Press CTRL+B.
13. Punch up the Midtones to 100 in the direction of your color.
14. Punch up Highlights to 25, 50, or 75. for your color.
15. Save.