Study On Reflectivity & Tubular Daylighting Systems

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 (NIR) range (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 product from Solatube reflected an average of 99.58% of the visible light, versus the two other brands which reflected 93.8% and 90.82%, 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% in the UV range, versus the other brands which reflected an average of 34.35 and 46.28%. At an 8-degree sun angle for the NIR range, Solatube produced an average specular reflectance of only 24.88% with each bounce, versus 96.98 and 90.67% for the other two brands. Solatube products also filter out 100% 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 

About Optical Reference Laboratory

The Optical Reference Laboratory is located in Davis, Calif.  UV/VIS/NIR spectral measurements are recorded using a PerkinElmer model Lambda 1050 spectrophotometer, with several sampling accessories available for reflection and transmission studies.  The resident spectroscopist is Bill Sweet, who served for more than 20 years as an applications scientist with PerkinElmer. During this time Bill acquired an interest in the use of high performance instrumentation in the optics and coatings industry, and his experience is now brought to bear on creating high quality standards and accurate measurements for customers.  For more information, visit www.opticalreferencelab.com 

About Solatube International

Solatube International, Inc., widely recognized as the daylighting industry innovator, has earned worldwide acclaim for its unrivaled ability to transform interior spaces with natural light and celebrated its 25th Anniversary in 2016. Based in California, the company is the leading manufacturer and marketer of tubular daylighting devices (TDDs) for all types of residential and commercial applications, and it continues to innovate with groundbreaking products that increase energy efficiency and light output, such as the award-winning Smart LED System and the high output SkyVault Series. For more information about the company and its related products, visit www.solatube.com or call 888-SOLATUBE.

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