These look useful. Particularly if you happen to want to attach them to a robot so that another robot can see it and charge towards it. As you do.
They might work well for light painting too. I saw them at the Science Museum yesterday in their gift shop. They are a set of battery powered coloured lights that you are supposed to attach to your fingers. You can find them on eBay (search for finger lights) at really stupid prices. I'm tempted to spend a tenner on 40 or so sets and go nuts with them.
I wonder how long the batteries last?