So, how exactly does HSL function? The lighting system is powered by a large, round solar light collector mounted on the office building’s roof. It resembles a satellite TV dish, but it is much larger and all of the light-collecting surfaces are mirrored. The collector in the test system is 48 inches in diameter. From sunrise to sunset, this collector follows the sun. Tracking the sun in this manner would have been prohibitively expensive twenty or thirty years ago. However, with GPS and computers, it is becoming much more affordable.

The goal is to direct as much sunlight as possible into the dish’s center. A large number of fiber optic light cables gather light at the center, as does a filter that blocks out unwanted and harmful UV and IR sunlight. There are 127 of these fiber optic cables in the test system, which then pass through a 4-inch opening in the building’s roof. The intensity of the light will decrease as it travels along the cables. However, the researchers believe they can run the cables up to 45 feet and still get plenty of light out the other end. This effectively limits HSL to one-story office buildings or the top floors of taller buildings, but the energy savings can still be significant.

A special lighting fixture at the inside end of the fiber optic cables diffuses the sun’s light in all directions. It resembles a fluorescent light fixture, except that the HSL light it emits is direct sunlight. A light meter is installed inside the lighting fixture so that when the sun is hidden behind a cloud or at night, conventional electric lighting can be used to compensate for the reduced HSL light. To keep the light intensity constant, you’ll need some traditional electric lighting. However, the advantage of HSL is that the sun is generally at its brightest during peak electrical usage hours, which are almost always midday.