I've wanted to try this for a long time. I took a bunch of photos in the dark with an extremely slow shutter speed (between 8 and 15 seconds). When the shutter was depressed, I took a couple of different coloured lights and swirled them around in various patterns. Here are a few of the results. Definitely something I'd like to experiment more with. Also, I'll need some more lights so that I can vary the colours!