A new public sculpture is being installed in Philadelphia -- one that will be completely invisible by day.

Montreal-based artist Rafael Lozano-Hemmer is now installing 24 searchlights along the Benjamin Franklin  Parkway that will create "Open Air," a canopy of light reaching from Logan Square to the Philadelphia Museum of Art.

Those powerful searchlights -- 240,000 watts of power, in total -- will create a matrix of beams that will constantly change shape, via vox populi. Anyone with an iPhone will be able to record a 30-second voice message that can be uploaded to a server. The high-powered beams will change position and intensity based on the sound of the voice.

The lights, occasionally, will also react to the frequencies of programmed bird calls. The temporary installation, from Sept. 20 to Oct. 14, will coincide with the annual southern migration.

Those pedestrians with iPhones on site will be able to hear the actual words that are controlling the light beams at that moment via the Open Air app.

Lozano-Hemmer has made large-scale public art out of light many times around the world, but this Philadelphia installation is the first time he will harness the power of the smartphone.

"It's true, I am a nerd," said Lozano-Hemmer, visiting Philadelphia to preview the piece. "But I don't use technology because it's new and original. I use technology because our politics, our economy, our communication is mediated for it. It's inevitable to use technology."

The installation will be global and inclusive. Anyone around the world can submit their voice through the project's website. However, the system will be able to detect local submissions based on the GPS in their smartphone. Those physically standing on the Parkway will be given priority.

Turning a light on U.S. immigration policies

The son et lumière is not without darkness, or politics. The piece has violent, militaristic undertones, as it is based on an invasive GPS surveillance system and spotlights commonly used by the military. The Mexican-born artist says the searchlights echo immigration policies along the U.S.-Mexican border.

"Open Air" was commissioned by the Association for Public Art -- formerly the Fairmount Part Art Association -- as a rare example of officially sanctioned temporary public art in Philadelphia. The spectacle will not have a chance to become commonplace.

"It creates the public. It brings them out from their home and gives them something to see and do," said Lozano-Hemmer. "It is not just a show or some kind of monument that represents one part of history, but rather it's about a platform for participation where people tell their own histories."

Most of Lozano-Hemmer's labors go into creating what the public does not see -- the complex, interactive functions. The website that will control the matrix of searchlights is now online, at OpenAirPhilly.net.