With Star Wars: The Force Awakens just hours away for most of us here in the States, here's a wonderful DIY tutorial from Shanks FX on creating an in-camera lightsaber effect using the original tools from Star Wars: Episode IV:
And about the tools he used:
If you want to try this out yourself, "Scotchlite" tape rolls can be found at local hardware store for around $10.
I also went in search of a Graflex flashgun handle and was lucky enough to find one but it was one from the 60s and not the sleek silver version that Luke uses in Episode IV & V.
The original effect is pretty spectacular when it works correctly, but the issue is that you need a light hitting the Scotchlite just right, or it just looks dull. Doing it the original way is rather cheap and not that time consuming, but if you want it to look like it does now in the films, you'll want to go with a rotoscoped post effect, which is how the effect is accomplished now. There are a million lightsaber post tutorials on YouTube, and I think it would be more productive to have you guys share what has worked for you, especially as software has changed and they aren't all as current as they could be.
Here's a great BTS video on lightsabers, and you can skip ahead to 4:35 in the video below for exactly what they did for the original trilogy:
Rotoscoping is certainly the way to go for the colored effect and to get a more spectacular hit if you were going to fight with them, but there is always something interesting about keeping things analog.
As an added bonus, here's another of the Star Wars related Shanks FX tutorials: