Hybrid Solar Lighting (HSL)

by Michael Russell - Date: 2007-04-17 - Word Count: 519 Share This!

Hybrid solar lighting (HSL) is a relatively new combination of older technologies that use a mirrored solar light collector and fiber optic light cables to directly bring outdoor sunlight indoors. When the sun is bright, no electricity is directly used to make the HSL light. The technology for this has been around for many years; but it has been very expensive and too subject to bright/dim variations in lighting as the sun goes behind clouds and out again.

However, with the recent development of inexpensive global positioning tracking and more affordable computer controls, direct fiber optic lighting is getting very close to being a cost effective reality for many office buildings. The U.S. Department of Energy has spent millions of dollars developing the prototype lighting systems and pretty much have all the bugs worked out. Now they are trying to get the cost down so that everyone can afford one of these lighting systems. The experts predict that you will see 10s of thousands of these lighting systems on office buildings around the world in the next 10 years.

So how exactly does HSL work? At the heart of the lighting system is a large, round solar light collector positioned on the roof of the office building. It looks a lot like a satellite TV dish, only much bigger and all the light collecting surfaces are mirrored. In the test system, the collector is 48 inches in diameter. This collector tracks the sun from sunrise to sunset. Twenty or thirty years ago, tracking the sun in this fashion would have been outrageously expensive. But today, with GPS and computers, it is getting to be much more affordable.

The idea is to focus as much sunlight as possible at the center of the dish. At the center there are a large number of fiber optic light cables to gather the light and also a filter to block out unwanted and harmful UV and IR sunlight. In the test system, there are 127 of these fiber optic cables that then go through a 4-inch opening in the roof of the building. As the light travels along the cables, the intensity will diminish. But the researchers figure they can run the cables up to 45 feet and still have plenty of light coming out the other end. This pretty much limits HSL to one-story office buildings, or the top floors of taller buildings, but the savings in electricity can still be substantial.

At the inside end of the fiber optic cables is a special lighting fixture that diffuses the sun light in all directions. It looks very similar to a fluorescent light fixture; except the HSL light coming out of it is direct sunlight. Inside the lighting fixture is a light meter so that when the sun is behind a cloud, or at night, conventional electric lighting can be used to compensate for the reduced HSL light. So you will need some conventional electric lighting to maintain constant light intensity. But the advantage of HSL is that during peak electrical usage hours, which are almost always midday hours, the sun is generally also at it's brightest.

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Michael Russell

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