A plastic panel that can harvest light when it hangs off the edge of a rooftop, redirecting sunshine down into dark urban streets below.

Cities keep getting taller as they run out of buildable space.  A record number of skyscrapers are planned in London, places like Bangkok and Panama City have dozens of new towers under construction, and Mumbai is building more skyscrapers than anywhere else in the world.

But while all of that density can help cities become more sustainable, it does create one obvious problem–there’s less and less natural light reaching city streets.

A fairly simple new device may help. Researchers in Egypt designed a plastic panel that can harvest sunshine when it hangs off the edge of a rooftop and redirect it down into dark urban canyons below. The panels don’t use any power–all of the work comes from the waving shape of the plastic itself. The engineers created a custom pattern that captures the maximum amount of light throughout the year.

The panels were inspired by Cairo’s own dim and narrow streets. “In Egypt, similar to many developing countries, this problem exists and actually started centuries ago,” says Amr Safwat, an engineering professor at Ain Shams University. Buildings in Cairo were originally placed very close together to help provide shade on hot days, but the buildings got higher and the streets got darker as the population grew.

Now, cities everywhere are facing the same challenge. “High-density development is becoming the norm,” Safwat says. “This significantly reduces the light that occupants have access to.”

The panels don’t use any power–all of the work comes from the waving shape of the plastic itself.

The panels can make a major difference. In simulated tests, the researchers found that the panels increased light on dark streets by 200 percent in the autumn and 400 percent in winter, when there’s the least sunshine.

Using the panels, dim rooms in adjacent buildings will finally be able get some natural light, which leads to a long list of benefits from lower energy use and increased property values to better health. In offices, studies have found that access to sunlight also helps make occupants happier, less stressed, and more productive.

The researchers are currently working on optimizing the design and plan to have a full-scale prototype ready this year.

Via Fast Company