Hello!! I know that there are many tuts out there for creating lightsabers, but there is such a variety of methods for creating lightsabers, but I think the best, and the easiest way is to make a white solid and rotoscope it over the actual prop saber, here's a screen shot i took while working to demonstrate the process. Watch this video by freddiew to get the full tutorial. Also, video copilot makes a great plugin for creating lightsabers, but i don't think it's really needed as the process can be done with all of the tools in AE. Here's the vid.