Redirecting sunlight to illuminate narrow streets

In a novel way to provide some natural light in dense urban centres with tall buildings around us, Egyptian researchers have developed a corrugated, translucent panel that redirects sunlight onto narrow streets and alleyways.

The panel is mounted on rooftops and hung over the edge at an angle, where it spreads sunlight onto the street below, a promising research reveals.

"We expect the device to provide illumination to perform everyday tasks and improve the quality of light and health conditions in dark areas," explained Amr Safwat, a professor of electronics and communications engineering at Ain Shams University in Cairo, Egypt.

Research has shown that lack of natural lighting can cause severe physiological problems such as serious mood changes, excessive sleeping, loss of energy and depression.

These dimly-lit areas specifically include narrow streets in developing countries, but the new panel could be used in any country as a greener, cheaper and more pleasant alternative to fluorescent and other artificial light.

While other commercially available window-like devices can redirect light, they are designed for shade and redirecting glare or for brightening a room - not a narrow street.

So the researchers decided to create their own design.

They wanted a simple way to redistribute natural light without the need for a tracking device that follows the rising and setting sun.

They designed a panel from acrylic plastic known as polymethyl methacrylate (PMMA).

Using simulations of sunlight shining on an alleyway, the researchers found that their panels increased illumination by 200 percent and 400 percent in autumn and winter, respectively, when sunlight is most limited.

The next step is to build a full-scale model 10 times bigger to validate their calculations and to test it in a real alleyway.

The team then plans to market and commercialise the panel.

Safwat estimates that a one-square-metre panel and a frame would cost between $70-$100 (Rs.40,00-6,000).

The paper was published in Energy Express, a supplement of The Optical Society's (OSA) open-access journal Optics Express.