Spray of Light

The 90-meter-high piece of graffiti scrawled on the back of this office building in Rotterdam, Netherlands, was the product not of hundreds of aerosol cans but of Laser Tag, an open-source painting program from New York City–based Graffiti Research Lab. As an ordinary green laser pointer’s beam was drawn across the building, a sensitive low-noise camera (developed for astronomers) captured its movements and relayed them to a laptop running the software. Then a movie projector ”painted” the squiggles onto the multistory canvas in real time.