The New Collimating Tubular Skylight (U.S. Patent No. 6,363,667)

Over the past three years, ENTECH, Inc., has developed and thoroughly tested a totally new concept in daylighting, the collimating tubular skylight shown above. This new concept uses an optimally tilted aperture to collect natural light from all parts of the sky. This collected light is then collimated by an expanding-area section of highly reflective tubing, and then delivered through a constant-area tube to the work area beneath the skylight. This redirection of the light from all parts of the sky to the work area beneath the skylight is called collimation.

Previous skylights, including tubular skylights, lack this collimation feature, and deliver much of their light output outside of the desired work area beneath the skylight. In fact, in our testing, we found a significant dark spot just beneath the skylight for these previous tubular skylights. Previous skylights are also inefficient, due to the large number of reflections required to deliver high-incidence light to the interior of the building. At each reflection, a substantial portion of the light is lost by absorption and scattering, even for highly reflective materials. ENTECH's new unit overcomes both of these deficiencies of prior skylight technologies.

The Collimation Feature

The basic function of the collimating section is shown in the sketch above. Rays of natural light can enter the skylight from all directions. In more technical terms, this means the rays can have an incidence angle of zero to 90 degrees, as shown by the different color rays in the sketch above. After a few reflections, these rays are collimated to emerge at much smaller angles - less than 30 degrees, as shown in the sketch. Thus the new skylight places the output light where it belongs, beneath the skylight, unlike earlier tubular skylights that do not control the output angles of the rays. This enables the lighting system designer to control the illumination pattern within the workspace, rather than accepting whatever nature provides. Stated more simply, if ENTECH's skylight is placed over your desk, it will illuminate your desk, and not your computer screen in the corner or your neighbor's office.

The collimation feature also allows the new skylight to use diffusers more effectively to eliminate glare and to provide uniformly pleasant light to the work space. With a special diffuser at the top of the skylight above the roof, and another 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.