3 Limitations of Tubular Daylighting Devices for Commercial Use

By Torrin Greathouse | May 21, 2015

With new technological advances in lighting materials and technology, a wide range of new daylighting products have emerged for commercial use. Tubular skylights are one. They utilize flexible, reflective light tubes to carry light into a building and penetrate through vaulted ceilings or curve around interior piping or other obstructions. No other skylights have these capabilities. They are adaptable to many building structures where other skylights would not be practical, such as in residential homes or small to medium size commercial spaces with low drop ceilings. However, there are three key limitations of tubular daylighting devices for use in commercial buildings.

Number of Devices Required

One of the reasons that tubular devices are so much easier to install than other skylights is their small size. Most tubular skylights are only between 10 and 21 inches in diameter, as opposed to other skylights which are on average between 2 and 8 feet across. Although these smaller skylights are more compact, more devices are required in order to adequately light a space. According to statistics published by the National Fenestration Rating Council (NFRC), tubular skylights typically use between 5-10% of the roof space. For larger commercial buildings, this will be a serious investment, involving the purchase of a high number of tubular skylight units and cutting many holes in the roof.

Diminishing Light Intensity

Tubular skylights carry reflected sunlight across long distances and around obstructions. This allows them to provide light despite overhead piping or HVAC systems below the roof, and it even allows light to be moved into lower stories of a building if necessary. However, any time light is reflected, a certain percentage is absorbed by the reflecting surface or scattered and diffused in many directions. Assuming that the light is coming in at an optimal angle, even the newest and most advanced reflective materials result in a 3% loss of intensity for every ten feet the light travels. While this may not be an issue for some installations, low ceilinged commercial buildings which require greater lengths of tube will experience diminishing light quality for every added foot of tubing or change in angle.

Passive Design

Tubular skylights are passive, which means that they are stationary and do not adjust to account for the sun’s changing location in the sky. While the transparent dome and reflective tubing of these skylights is intended to catch the most sunlight possible, these features become less effective as the sun falls closer to the horizon. This is because when the sun is lower, the light must reflect more times before reaching the building’s interior. Each added reflection per foot decreases the amount of light the building receives.

While tubular daylighting devices do come with these potential pitfalls, they are still an excellent option on the market today. Their small size and flexible tubing allows them to be installed in unique ways, although the installations tend to be appropriate only in much smaller spaces.

Ciralight manufactures a solar-tracking skylight, the Ciralight SunTracker™. This active system is designed for large-scale facilities, including commercial buildings. It uses a combination of solar power and GPS technology to provide completely free and off-the-grid natural sunlight for up to 10+ hours per day. SunTrackers™ save energy, lower utility bills, and illuminate rooms with healthy, abundant, natural light.

(Photo: Gavin Schaefer, CC)

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