Everyone knows that downtown alleyways are dark at night, but even in the daytime, shadows cast by the tall buildings on either side can make them quite gloomy. While that might not matter much for little-used alleys, it's certainly a factor in cities where people live and work in them. That's why researchers from Egypt's Ain Shams University are developing a new type of panel that diverts sunlight from buildings' roofs down into the alleyways beside them.

The translucent panels are made from polymethyl methacrylate, which is the same acrylic from which Plexiglass is made. While the underside of each panel is flat, the top surface is composed of a series of parallel ridges that take the form of a sine wave when viewed in cross section. These ridges serve to capture sunlight from a wide range of angles, so the panels don't need to pivot with the sun like a heliostat, or be repositioned for different times of year.

Gathered light travels through the acrylic and is emitted at the panel's edges, one of which hangs over the side of the building's roof at a downwards-sloping angle. In computer simulations, the scientists found that use of the panels on a given alleyway would increase illumination by 200 percent in autumn, and 400 percent in winter – which are the two seasons when alleys receive the most shade.

A small prototype was also tested over a 0.4 x 0.4-meter (1.3 x 1.3-ft)-wide shaft measuring 1.2 meters (3.9 ft) deep, and it worked as expected.

Lead scientist Prof. Amr Safwat now plans on building a panel 10 times larger than the prototype, and testing it on a real alleyway. He ultimately hopes to market the panels, and estimates that a panel and frame measuring one square meter (10.8 sq ft) should cost between US$70 and $100.

A paper on the research was recently published in the journal Optics Express.

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