Home > Uncategorized > Daylighting Facts: Part 1

Daylighting Facts: Part 1

January 24, 2014 Leave a comment Go to comments

Thanks go to our friends at Solatube for providing up-to-date educational materials for us to share with you to help you better understand the superior quality of a Solatube product.

Performance characteristics of Tubular Daylighting Devices (TDDs) can vary greatly, depending on the materials used and the sophistication (or lack thereof in the case of some manufacturers) in the engineering of how the various product components work cooperatively together. Understanding the key performance indicators—such as surface spectral and Specular Reflectance, light collection selectivity and throughput / output, solar heat gain and ultraviolet (UV) blocking—and their relevance to the system’s overall performance will help you select the best daylighting solution for your building project.

The most crucial aspect to understand is the difference between Total Reflectance and Spectral Reflectance. These two terms are often confused because they are both measures of light reflection, but they are certainly not interchangeable.

Total Reflectance vs. Specular Reflectance

specular reflection
The reflection of light is extremely predictable. When light strikes a surface, it is either absorbed or reflected. Total Reflectance indicates the percentage of light that is reflected, regardless of the direction it travels after leaving the surface.
A surface’s Total Reflectance can consist of both specular and diffuse components. To illustrate this, imagine a ray of light as a tight bundle of smaller, individual rays, all traveling parallel to each other. In accordance with the Law of Reflection, rays that strike a smooth surface will reflect and remain in a concentrated bundle. This is called Specular Reflection and represents a “mirror-like” reflection of light. On the other hand, rays that strike a rough, or diffuse, surface will reflect and scatter in many directions through Diffuse Reflection.
While a diffuse surface can have a high Total Reflectance, the reflected light is scattered, which prevents it from being transmitted in a consistent and tightly-controlled fashion. For TDDs, a high Specular Reflectance is imperative so that light can be efficiently transferred through the system. A Diffuse Reflectance should be avoided since that would result in light being scattered and lost back out through the top of the system.

For more information on any Solatube product, call the Specified Building Products team at (877) 903-9090

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