When people talk about passive solar energy, what usually comes to mind is the orientation of construction sites for maximum heating in winter and cooling in summer. Orienting buildings to make the most of the sun is an ancient practice, but there are other passive uses of sunlight that are just as ancient. Solar heating of water and various methods of bringing sunlight into houses for lighting purposes have been practiced by cultures dating back to the ancient Egyptians.
Skylights and atriums are the most familiar use of the sun to light the home, but another method used in ancient Egypt is less well known. Known, variously, as ‘light tubes’, ‘tubular skylights’, ‘light tubes’, ‘sunscoops’ or ‘solar tubes’, in their original form they were narrow shafts, sometimes lined with reflective material to better reflect Sun. These are best known for their use in the tombs of the ancient Egyptians, bringing light into the depths of their hidden chambers.
Modern solar tubes date back to the prismatic light guide patent in 1981, although before electric lights, Paul Emil Chappuis patented and marketed a similar design beginning in the 1850s. His reflectors, designed to send light into depths of the buildings, were in production until their factory was destroyed in World War II. The solar tube in its most common form became commercially available in 1991. In 1998, a European Union research project called ARTHELIO began investigating hybrid lighting systems that combined artificial light (the ‘art’ part of the acronym) with a Heliostat system to distribute natural light. The project continued until 2004 and resulted in two demonstration projects.
Despite modern research on hybrid systems, the basic idea of the solar tube is simple and relatively easy to implement. Marketed as light tubes or tubular skylights, these solar tubes, unlike traditional skylights, do not require extensive rebuilding work and the comparatively small opening is less subject to leaks and other problems associated with their larger siblings. They require minimal space, making them ideal for closets or bathrooms, and can be installed on any type of ceiling. Kits, along with detailed instructions, are available at home improvement centers like Lowes or Home Depot.