Hybrid Solar Lighting: Sunlight without windows

February 17, 2008 6:56:21 PM PST
A handful of buildings in California are beginning to try a new kind of indoor lighting: Sunlight without windows.

It's called Hybrid Solar Lighting. It's half solar and half electric. During the day, sunlight pours out of the light fixture; at night, a conventional light bulb takes over. So it's a hybrid.

How do you get sunlight to the fixture? With bundles of optical fiber--light pipes leading up to the roof. On the roof is a large dish that does not point at a satellite; it points at the sun. It concentrates the sun into the end of the fiber bundle.

The sunlight bounces twice. Once, off the big mirrored dish, then off of a smaller secondary mirror, which focuses everything down into the fiber optics. The mirror actually filters out the ultraviolet and the infrared rays. You don't have to worry about getting sunburned indoors.

What makes it practical are new plastic fibers and a sophisticated tracking system that points precisely at the sun, no matter the time of year.

There is even a psychological benefit, according to Kostas Papamichael, Associate Director of the California Lighting Technology Center in Davis. "We know that people like daylight," he says. "We know that daylight gives the best color rendering. It links us to the environment and satisfies biological needs that we have. Not necessarily at the level that you get it from a window -- and, next to it, by a skylight -- but some connection to the exterior for sure."

For our interview, we lit Kostas Papamichael entirely with sunlight from the roof, bright and clear. What's not so clear is the cost benefit. The California Lighting Technology Center is conducting an independent scientific study for the developer, Sunlight Direct. So far, it looks good, especially in a hybrid configuration. What looks like a fluorescent light bulb is actually a single, huge optical fiber. Install the fiber alongside a real fluorescent lamp and you have a 24-hour solution -- a hybrid light to go with your hybrid car.

So far, the only place you can see hybrid solar lighting is Tennessee and in a few businesses in Davis, but a home version should be available next year.

CHECK OUT THESE LINKS

CALIFORNIA LIGHTING TECHNOLOGY CENTER
Website: http://cltc.ucdavis.edu
Phone: 530-757-3444 (Davis, CA)

SUNLIGHT DIRECT
Website: http://www.sunlight-direct.com
Phone: 865-483-6624 (Oak Ridge, TN)

SACRAMENTO MUNICIPAL UTILITY DIVISION (SMUD)
Demonstration open to the public in main building lobby.
Website: http://www.connectmyelectricity.com


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