Writing with light on a long exposure is a lot of fun, especially since the results are always a nice surprise and although it takes a little patience, with a bit of experimentation, its better than using the sometimes fake looking photoshop effects available. Below are a couple of examples.
Inspired by my recent trip to the Astronomy Photographer of the Year exhibition, I used a torch spun round on a piece of string to create the bands of light which represent the path of an electron. I then overlaid my favourite image of the horsehead nebula which reminds us of the fact that we are created from elements made deep in the heart of burning stars. A nude female sits at the centre of the atom representing birth and creation.
The below image was created by running around the model with a torch. The model needs to stay extremely still, since this is one long exposure.