If you live in San Francisco, you may have seem some otherworldly lights radiating from the train tracks near your house this summer. If so, you can take off your tin foil hat: It was just the latest project of Aaron Koblin, the Creative Director of Google’s Data Arts Team, and director Ben Tricklebank.

You might remember Koblin from his interactive visualizations (he created the interactive video for the Arcade Fire's Wilderness Downtown), and Tricklebank heads up the production company Tool. But this summer, the duo are taking part in Station to Station, a train full of artists and musicians that's winding its way across the country putting on art shows and concerts. Their contribution, an experiment called Light Echoes, ties into train travel in a very literal way.

Light Echoes is a digital printer of sorts—but only by the most conceptual definition. It’s a high-powered laser attached to a wheeled boom, which rolls along the train tracks at a fixed speed. The laser projects light onto the surrounding landscape, one pixel at a time. In person, it looks like a brief trail of LED light. But captured in long-exposure photographs (using a Red EPIC camera), the projections form cohesive images—anything from a pattern to a quote from Walt Whitman. The contraption literally prints in light, thanks to train infrastructure laid down decades ago. According to Koblin, who emailed from the train’s Minneapolis stop last night, it casts “visual echoes of the train's presence cast upon the landscape.”

A Railroad-Mounted "Printer" That Covers Its Tracks in Laser Graffiti

Because the boom setup is so elaborate—you can see some progress shots on Wired—it won't actually be accompanying Koblin aboard the Station to Station train this week. Instead of dragging the custom contraption behind the train, they'll be showing a film of the project (seen above). But that doesn't mean they're done with Light Echoes. “Our original hope and desire was to make it focused around visualizing live performance,” Koblin says. “I'm really optimistic that we'll be able to take this idea to its next iteration. Light Echoes has been a big experiment and we've learned so much.”

Station to Station's next stop is Santa Fe, with performances by Cat Power and art by Carsten Höller. Check out the full lineup here.

A Railroad-Mounted "Printer" That Covers Its Tracks in Laser Graffiti

A Railroad-Mounted "Printer" That Covers Its Tracks in Laser Graffiti

A Railroad-Mounted "Printer" That Covers Its Tracks in Laser Graffiti