When people talk about passive solar energy what usually comes to mind is the orientation of building sites for maximum heating in the winter and cooling in the summer. Orienting buildings to take maximum advantage of the sun is an ancient practice, but there are other passive uses of sunlight which are just as old. Solar heating of water and various methods of bringing sunlight into houses for lighting purposes have both been practiced by cultures as far back as the ancient Egyptians.
Skylights and atriums are the most familiar use of the sun for lighting in the home, but another method used in ancient Egypt is less well known. Known, variously, as ‘light tubes', ‘tubular skylights', ‘light pipes', ‘sunscoops', or ‘solar tubes', in their original form they were narrow shafts, sometimes lined with reflective material to better reflect the sun. These are best known for their use in the tombs of the ancient Egyptians, bringing light deep into their hidden chambers.
Modern solar tubes date from the patenting of the prism light guide in 1981, although back before electric lights a similar design was patented and marketed by Paul Emil Chappuis, starting in the 1850s. His reflectors, designed to send light deep into buildings were in production until his factory was destroyed in World War II. The solar tube in its most common form began to be commercially available in 1991. In 1998 a European Union research project called ARTHELIO began to investigate hybrid lighting systems combining 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.
Modern research on hybrid systems notwithstanding, the basic solar tube idea is simple and relatively easy to implement. Marketed as light tubes or tubular skylights, these solar tubes, unlike traditional skylights, do not require major reconstruction work, and the comparatively small opening is less subject to leakage and other problems associated with their larger brethren. They require minimal space, so they are ideal for closets or bathrooms, and can be installed on any type of roof. Kits, along with detailed instructions, are available from home improvement centers such as Lowes or Home Depot.