Check out this video from the Graffiti Research Lab at Eyebeam OpenLab—it shows an installation of LED Throwies in action on a street corner in West Chelsea, Manhattan (never mind where you've heard the soundtrack before). What's an LED Throwie? It's a lithium battery, a 10mm diffused LED and a rare-earth magnet taped together. You throw them on to anything metal to add a splash of light and color. The result is reconfigurable, night compatible, digital graffiti. Here's how to make your own.
Photo via Urban Data in the Graffiti Research Lab pool