Five Myths of Tubular Daylighting Devices

Are these myths preventing you from specifying/purchasing tubular daylighting devices for your commercial facility?

Michael Sather, commercial marketing manager at Solatube International Inc., Vista, CA

Michael Sather, commercial marketing manager at Solatube International Inc., Vista, CA

Many people are familiar with the concept of tubular daylighting devices (TDDs), often generically referred to by more informal names such as solar tubes, sun tunnels, light pipes, or tube lights. The general concept is simple: A dome, attached to a roof with a self-mounted flashing or mounted on a curb, captures sunlight, transfers it into the building through a highly reflective tube, and delivers it into the interior space through a diffuser lens mounted at the ceiling level or at the end of the tube in an open ceiling.
   In the past 13 years, TDDs have revolutionized the way buildings are illuminated. When applied correctly, a building can be fully daylit using only the natural light supplied by the TDDs for 90% or more of the occupied hours of the year, relying on electric lights only as a backup during extremely overcast days or at night.
   That said, how do you know if TDDs are the right choice for daylighting your project? What key aspects should you consider when selecting the best TDD for a specific application? To help answer these questions and give you a better understanding of this product category, let’s explore five myths of TDDs.

When applied correctly, a building can be fully daylit using only the natural light supplied by the TDDs for 90% or more of the occupied hours of the year, relying on the electric lights only as a backup during extremely overcast days or at night.

When applied correctly, a building can be fully daylit using only the natural light supplied by the TDDs for 90% or more of the occupied hours of the year, relying on the electric lights only as a backup during extremely overcast days or at night.

Myth 1: Tubular daylighting devices are only for residential applications or small spaces.
The original TDDs that appeared in the U.S. market in the early 1990s were strictly designed for residential spaces. In the past two decades, the TDD category grew to rival and eventually surpass traditional skylights for residential applications.
   Building on that residential-market success, the world’s first commercial-grade TDD appeared on the scene in the year 2000. This new technology boasted a 21-in.-dia. tube and a transition box for a grid ceiling system, which allowed a round tube to accommodate a square diffuser, simply by replacing a 2 x 2-ft. ceiling tile. Open-ceiling models also debuted at this time and featured a diffuser lens attached directly to the tube bottom. As a result, the approach to daylighting commercial buildings was greatly simplified and the daylight fixture concept was born.

Specular reflectance, which refers to a concentrated bundle of light transferred down the tube through the diffuser, is the key factor in determining how effective a TDD is at delivering light to an interior.

Specular reflectance, which refers to a concentrated bundle of light transferred down the tube through the diffuser, is the key factor in determining how effective a TDD is at delivering light to an interior.

Myth 2: Tubular daylighting devices are only for the top floor.
Specular reflectance, which refers to a concentrated bundle of light transferred down the tube through the diffuser, is the key factor in determining how effective a TDD is at delivering light to an interior. It is often confused with total reflectance, which refers to scattered light that is reflected in every direction. Total reflection is not an indicator of throughput since this would include light reflecting back up the tube.
   When daylight moves through a TDD, it reflects (or bounces) off the tubing surface. With each bounce, a small amount of that light is lost. For each 90-deg. turn, only about 5% of the light is lost. This makes possible tube runs of great distances, spanning multiple floors, running down chases in the walls, and using multiple 90-deg. turns to be able to deliver daylight deep into the interior of multistory buildings.

When daylight moves through a TDD, it reflects (or bounces) off the tubing surface. With each bounce, a small amount of that light is lost. For each 90-deg. turn, approximately only 5% of the light is lost.

When daylight moves through a TDD, it reflects (or bounces) off the tubing surface. With each bounce, a small amount of that light is lost. For each 90-deg. turn, approximately only 5% of the light is lost.

Myth 3: Tubular daylighting devices are only effective at certain times of the day or year.
Factors affecting seasonal consistency are a combination of specular reflectance, dome optics, spectral selectivity, color temperature maintenance (CTM), and solar heat gain. Lower end TDDs will have a greater difference in daily and seasonal variation due to a lack of the above mentioned properties.
   Advanced TDDs offer daily and seasonal consistency by incorporating dome technologies with passive internal reflectors or Fresnel-lens optics to help efficiently collect low-angle sunlight. This can greatly increase performance in the early morning or late day. During the winter months, when the sun is low in the sky, this is an especially important consideration in Northern latitudes.

Myth 4: Tubular daylighting devices are unpredictable.
While dome optics and tubing material will play a major role in the predictability and consistency of a TDD, you must also take into account the overall design. Even the most advanced TDDs can be designed incorrectly into a space. If you use too many units, the results can be overwhelming; if you use too few, the results can be disappointing. Most TDD manufacturers offer daylight dimming devices that provide total control over the amount of daylight entering the space.

Myth 5: All tubular daylighting devices are the same.
This statement is equivalent to saying all cars are the same. To ensure you select the right TDD for your particular project needs, there are three main considerations: the manufacturer, the product, and the partner:

  • The manufacturer. Significant differences exist in the product offerings and core focus of companies manufacturing TDDs. Some manufacturers specialize in TDDs as their sole business, whereas other companies may only offer TDDs as a small part of their overall product line.
  • The product. Be sure to specify a product that meets the needs of the space. Most TDD manufacturers will offer a wide range of models and component options to create the right configuration for the specific application and climate.
  • The partner. Once a manufacturer is selected, it is probably best to make sure there is a factory-trained distributor or representative to assist with the project. Most TDD manufacturers will have a partner who works with you at a local level from project conception through completion to help you meet your daylighting goals and stay within your budget. These companies typically offer installation services as well as installation training for subcontractors to ensure your project is a success.

Michael Sather is the commercial marketing manager at Solatube International Inc., Vista, CA.

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