The First Full-Scale Installation
In the ENTECH, Inc., Conference Room

In January 2000, for our first millennial shareholders meeting, we installed two full-size 15-inch collimating tubular skylights in our conference room. The photo above shows the outside view of the two light-collecting apertures on the steel roof of our headquarters building in Keller, Texas. These apertures are tilted by 35 degrees toward the south, to maximize light collection over the entire year. (Our latitude is about 33 degrees.) Under the clear, tough, weatherable, hail-proof acrylic plastic outer glazing on the light-collecting aperture of each skylight, a very special diffuser (made by 3M) is used as a second glazing to minimize heat gain or loss and to prevent glare by diffusing the sunlight. This second glazing consists of an array of wide-angle Fresnel lenses. The light collected by each aperture and diffused by the Fresnel lens array is reflected into the collimation section of the tubular skylight, and then downward into a square-section tube, which delivers the light to the luminaire in the conference room.

Beyond Expectations

The photo above shows the two skylight luminaires in our conference room. The luminaires are standard 24-inch square openings to match conventional suspended ceiling frame dimensions. Each luminaire is equipped with a special lens diffuser unit just like the one used below the outside aperture above the roof. This diffuser provides exceptionally uniform illumination to the room, and presents a striking, crystalline visual appearance.

Although we had thoroughly tested prototype units before installing these two skylights in our conference room, we have found the units to perform beyond our expectations. We expected these two units to reduce our fluorescent electical lighting costs by about 33% during the work day. Since this 320 square foot conference room used about $1.50 per day in electricity to power the fluorescent lights before we installed the skylights, we hoped to save about 50 cents per day. We expected to need some fluorescent lighting contribution early and late in the day on clear days, and throughout the day on cloudy days. But we have found that the room is completely usable and comfortable throughout the day without any fluorescent lighting contribution, except during the dark-cloud periods during severe Texas weather. Thus we rarely turn on the fluorescent lights, even in their lowest dimmed mode. Furthermore, we were worried about having to cover the skylights for slide or viewgraph presentations. But, since the new skylight places the output light where it belongs, beneath the skylight on the conference room table, the walls are less brightly illuminated, and projected information is easy to read without covering the skylight luminaires.

As expected, the new skylight provides a glare-free, uniformly pleasant light to the work space. With the special lens diffusers used near the top of the skylight above the roof, and at the bottom of the skylight in the ceiling luminaire, a beautiful, smooth, full-spectrum illumination profile is provided under all sky conditions. While the intensity varies with the sun's position and cloud conditions, the illumination pattern remains smooth and pleasant.