LED throwie – it sounds like a children's cartoon, doesn't it?
Okay, maybe not, but they're fun to make. You tape an LED to a battery, maybe add some magnets to the battery so that it sticks to something metal. Done. Like these:
Besides them costing about a buck a pop to make, this is a very guerilla way to graffiti something made of metal. Now hopefully you'd clean them up when they were dead, but I'm an optimist. What's most excellent is when a bunch of people come together for the specific purpose of making some light art with these throwies – check out this video:
The Graffiti Research Lab, which does a bit of light art and lighting-related graffiti, made these LED throwies popular. Check out their website, and check out Eyebeam Openlab, the folks who organized the event in the video.