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Study Compares Reflectivity Among Leading Tubular Daylighting Systems


3/15/2017

A recent third-party study conducted at Optical Reference Laboratory compared tubing reflectivity among three leading brands of tubular daylighting device (TDD) systems. The study measured reflectivity of materials used in daylighting systems in the human vision range, light we can see; near infrared range (NIR), what we experience as heat; and the potentially harmful UV range, that can cause discoloring and fading of materials and surfaces.

In the category of human vision range, Solatube International scored the highest for specular, mirror-like, reflectivity at three different incidence angles, representing different angles of the sun; 8, 40 and 60 degrees. For example, at the 8-degree incidence/sun angle, the Spectralight Infinity with cool tube technology from Solatube reflected an average of 99.58 percent of the visible light, versus the two other brands which reflected 93.8 percent and 90.82 percent, respectively. The human vision range is what drives how we see and perceive our environments and is the desirable type of light that we wish to bring into our homes and businesses.

Overall, for a typical 10-foot TDD application, early-morning daylight entering a tube at an 8-degree incidence angle may make 56 bounces before exiting at the ceiling diffuser. As a result, seemingly small differences in specular reflectance can have enormous impacts on daylighting potential, especially when our bodies crave daylight to go along with our morning coffee. In this early morning daylight case, Solatube’s output/performance was 400 percent better than brand A and 20,000 percent better than brand B.

Conversely, in the UV and NIR ranges, Solatube International reflected less of the undesirable types of light. At the 8-degree incidence angle, Spectralight Infinity produced an average specular reflectance of 27.17 percent in the UV range, versus the other brands which reflected an average of 34.35 and 46.28 percent. At an 8-degree sun angle for the NIR range, Solatube produced an average specular reflectance of only 24.88 percent with each bounce, versus 96.98 and 90.67 percent for the other two brands. Solatube products also filter out 100 percent of UV rays at the dome level, removing the harmful UV rays even before they enter the Spectralight Infinity Tubing system.

The study concluded that Solatube’s Spectralight Infinity gave superior performance in several ways, compared to the other brands that were tested. The Solatube product delivers more of the daylight that lights up an interior space and less of the light that can create heat gain or sun damage.

An executive summary of the study is available here: https://www.dropbox.com/s/j1qoxzbqiwp8gz1/Summary%20of%20Reflectivity%20Study.pdf?dl=0


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