Egyptian researchers have been working on optical devices that could bring natural light into dark, highly populated areas. The 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.
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.
What they came up with is a panel made of polymethyl methacrylate (PMMA), the same acrylic plastic of which Plexiglas is made. The bottom of the panel is smooth while the top is covered in ridges that are based on a sine wave, the mathematical function that describes everything from light to pendulums. The researchers used computer simulations to find the size and shape of the grooves that distribute the most amount of sunlight in a wide range of sun positions all year round, whether it's high or low in the sky. A sine-wave pattern is also easy to manufacture.
Using simulations of sunlight shining on an alleyway, the researchers found that their panels increased illumination by 200 and 400% in autumn and winter, respectively, when sunlight is most limited. They also tested a small prototype over a 0.4-meter-by-0.4-meter shaft that is 1.2-meters deep and found that it lit up the area as designed.
The next step will be 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 commercialize the panel. He estimates that a one-square-meter panel and a frame will cost between $70 and $100.
He also noted that using sunlight to illuminate historical places—such as ancient alleyways in Egypt—also helps preserve the authenticity of the site, maintaining its cultural value and historical significance.
This work was funded by the Science and Technology Development Fund of Egypt.
Paper: “Illumination of dense urban areas by light redirecting panels,” S. I. El-Hanawy, et al., Optics Express, Vol. 22, Issue S3, pp. A895-A907 (2014).
Photo: A simulation of the illuminance of an alleyway at noon at two different times of year, autumn (top) and winter (bottom). The new light-directing panel increases the amount of light that reaches the alleyway, as indicated by the higher amounts of red and yellow in the right-hand images (“with panel”) compared to the left-hand images (“without panel”). Credit: Optics Express.