Fiber Optics for Daylighting
High-Tech "Active Daylighting" a Pricey But Cool Option for Bringing Natural Light Into Dark Interiors
Fiber optics, that miracle of modern communications, can also be used to deliver natural light to spaces deep in a building.
Last week I focused on tubular skylights, which provide a great way to bring daylighting into home offices, hallways, bathrooms, and other spaces. An aluminum tube that’s highly reflective on the interior transmits daylight down through an unheated attic to the space below—delivering the light through what appears to be a fairly standard light-diffusing ceiling fixture.
It’s a great technology—especially with the relative low cost—but it has some limitations. You need a relatively straight shot, and it’s hard to extend the tubes through living space to reach first-floor spaces in multi-storey buildings.
For those with deep pockets, “active daylighting” using fiber optics provides a way to bring daylight deep into a home or commercial building—beyond the reach of tubular skylights. I know of two companies that are offering this technology: the Swedish company Parans Solar Lighting, AB (through its U.S. distributor HUVCO Daylighting Solutions), and the Himawari Solar Lighting System from La Foret Engineering Company, Ltd. in Tokyo, Japan.
Here’s how the Parans system works: On the roof or an outside wall, there’s a one-meter-square collector (the SP2) with 62 separate Fresnel lenses that track the sun as it moves across the sky. The SP2 uses about 2 watts of electricity to operate this tracking, which is controlled by a photosensor and microprocessor.
Each of the lenses concentrates the sunlight into a tiny optical fiber, just 3/100ths of an inch (0.75 mm) in diameter. Bundles of 16 of these optical fibers are aggregated into cables (four from each SP2) that are about a quarter-inch (6 mm) in diameter. These cables can be run up to about 65 feet (20 m) to bring natural light to interior spaces quite distant from the roof or windows. The cables can be run through interior wall cavities, ceiling plenums, or wiring chases, and their bending radius can be as tight as two inches! The greater the length, the greater the light loss: at 33 feet (10 m) 64% of the light is delivered; at 65 feet (20 m), only 40%.
In the spaces where light is to be delivered, various fixtures are available. These include spotlights, fairly conventional-looking ceiling fixtures, and some hybrid fixtures that include both daylighting and high-efficiency fluorescent lighting. Some fixtures are served by just one optical cable; others by two or four.
The Parans system is far from inexpensive, with a system starting at about $10,000 for one SP2, four optical-fiber cables, and four fixtures, plus installation. To date, about 20 of these systems have been installed in the U.S., according to HUVCO.
Now, if you think that’s expensive, there’s another system available, at least in Japan. The Himawari Solar Lighting System (named after the Japanese word for sunflower) is a similar, but larger, fiber-optic system that uses tracking Fresnel lenses to capture sunlight and distribute it through a building. The product was first demonstrated in the late-1970s, and over 1,000 of these systems have been installed in Japan and Western Europe since then. Larger installations can cost over $100,000.
Distributed daylighting through optical fibers is an exciting high-tech approach to making use of natural light. If prices come down, this could become a much more practical strategy in the future.
One interesting issue with distributed daylight, according to an expert I spoke with, is that the color of the light changes throughout the day. In the early morning and late afternoon, it can be distinctly orange, while in the middle of the day, it can be quite blue, which gives the light a cool feeling. Some will find this annoying, while others may appreciate the experience of light quality changing during the day—as occurs outdoors.
For more information on Parans Solar Lighting, contact HUVCO at 800-832-6116. I was unable to determine whether the Himawari is available in North America, but will provide that information in a comment if I hear back from the company.
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