The basic principle is you work in a dark room, turn your camera so it has a long exposure length and then wave a light source around. You can end up with some pretty impressive images.
Ben Cowell-Thomas was keen to use the technique to create a stop motion animation. The difficulty in doing that successive photos had to be very similar if he wanted the animation to be smooth. You really need something that can perform the movements in an accurate and repeatable manner.
Cue the robot :)
He started with a LEGO NXT setup, that controlled a laser pointer. He wrote a custom python script that takes a model from Maya, converts it to a path and then sends position commands to the NXT rig via Bluetooth.
Ultimately without accurate position control (NXT's are great for velocity control) he struggled to get the accuracy he needed. It is great however, to see the use of NXT's as a quick and (relatively) simple prototyping system.
After learning a lot about what worked and what didn't, he ended up with a beautifully rig.
Check out the end results, just beautiful!
Find a complete rundown of the project here - http://www.rethinkfx.com/projects/making-of-lightplot