Sunlight on Demand

Let the sun shine in, in as many ways possible. The influential 1977 design book A Pattern Language by Christopher Alexander, Sara Ishikawa, and Murray Silverstein suggests that rooms should be illuminated by two sources of natural sunlight, ideally placed perpendicular to each other. The openings (usually windows or doors, but also skylights and even transoms) should be arranged to give as much uniform light as possible. But not every room has windows, and interior hallways are naturally ill-lit. One method is to transport concentrated sunlight to the interior of a building through fiber-optic cables.

Invented by Dr. Duncan Earl, a researcher at Oak Ridge National Laborarory, this type of lighting system uses a polished parabolic dish mounted on a building’s roof to track the sun and focus its light onto a bundle of fiber-optic cables. The cables carry the sunlight throughout the building, terminating at overhead lighting fixtures containing fiber-optic diffusers that spread the sunlight around. The chief advantage of this system over conventional skylights is that over the course of a day, regardless of the sun’s position, the fiber optics convert its light into constant uniform lighting (except, of course, at dawn or dusk).

On a sunny day this lighting system can transmit 50,000 lumens, the equivalent of thirty 100-watt lighting fixtures, more than enough to illuminate a 1,000-square-foot home. On less than perfectly sunny days, or at twilight, a small sensor in the fixture measures the available sunlight and turns on auxiliary fluorescent lights to provide uniform lighting. Earl estimates that one hybrid lighting unit can save a building approximately 8,000 kilowatt hours per year (which works out to about $750 in lighting costs).

The system hinges around Oak Ridge’s recent devel­opment of high-heat, low-cost plastic fiber-optic cable. However, since plastic fibers only transmit about 50 percent of the available light, hybrid lighting only really works in one-story buildings, or on the top floor of multistory buildings. After testing the product in multiple locations, the difficult part, Earl acknowledges, lies in developing a fiber-optic cable that’s transparent enough to extend the system to other floors, yet inexpensive enough to be cost effective.