Frequently Asked Questions
Light Transfer Efficiency (LTE) measures how effectively and consistently daylight is transferred through a TDD’s optical tubing system and into a room for all daylight hours of the year. This factor is closely linked with the specular reflectance associated with a system’s tubing material. The higher the specular reflectance, the more efficient and consistent the transportation of light is. A high LTE typifies a product that limits light loss and, therefore, delivers an even and dependable amount of light to an interior, regardless of season or weather condition.
The ability of a tubular daylighting device to capture low-angled winter light may differ significantly from its ability to capture high-angled summer light. The ratio of summer to winter light output can be an indicator of the product’s effectiveness in delivering (or not delivering) consistent light throughout the course of a year. Solatube® Daylighting Systems will produce uniform levels of output regardless of season (or climatic conditions), resulting in steady and reliable interior illumination despite variations in exterior conditions or seasonal changes in the daylighting resource.
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 tubular daylighting devices (TDDs), a high specular reflectance is imperative so that light can be efficiently transferred through the system. A tubing system with a diffuse reflectance component should be avoided since that would result in light being scattered and lost back out through the top of the system.
The Spectralight® Infinity Tubing used in Solatube® Daylighting Systems is the most reflective material used in TDDs. With an extremely high specular reflectance of up to 99.7%* over the visible portion (ranging between 380-760 nanometers (nm)) of the electromagnet spectrum, it ensures that very little light is lost as it travels through the optical tubing system.
Achieving a high specular reflectance is critical since even small differences in reflectance values can significantly impact light output. That’s because every time a ray of light is reflected, some amount of that light is either scattered or lost through absorption. The difference of just a few percentage points in specular reflectivity makes a huge difference in overall performance.
Contrary to total reflectance, specular reflectance is a key factor in determining an optical tube’s efficiency in transferring light, and manufacturers should provide specular reflectance data to document the true efficiency of their TDD systems.
*Specular reflectance greater than 99%, with wavelength-specific reflectances up to 99.7% for the visible spectrum
Under the product warranty, Solatube® Daylighting System components are covered for 10 years, most electrical components for 5 years, and Solatube Smart LED™ electrical components for 3 years. For full warranty details, click here.
To answer this question, we first need to understand what wavelengths of radiation are emitted through a Solatube® Daylighting System. Solatube Daylighting Systems utilize two technologies to eliminate ultraviolet (UV) radiation and reduce heat from infrared (IR) wavelengths entering the building interior.
The first technology is related to the domes. Solatube acrylic outer domes have special UV inhibitors designed to block 100% of UVB (280 to 315 nanometers), 100% UVC (100 to 280 nanometers) and 98.5% UVA (315 to 400 nanometers) rays.
The second technology is related to the tubing. Spectralight® Infinity Tubing transmits the visible spectrum of light (400 to 760 nanometers). A minimal amount of the infrared spectrum of light (above 760 nanometers) is transmitted by the Spectralight Infinity Tubing.
With this information in mind, the following subjects can be addressed.
In conjunction with the above information, there are a few factors to consider when determining if a Solatube Daylighting System will have an effect on plant growth. The first factor is how much UV, if any, the particular plant will need for proper growth. Second, the size of the daylighting system used may impact how much light the plant can obtain. It is also important to point out that the Solatube Daylighting System removes a majority of the infrared wavelengths, which substantially reduces any heat-related stress problems that may occur with indoor plants.
Typically plant growth occurs between 400 and 1000 nanometers. Based on this data, it would be safe to say that, in general, a Solatube Daylighting System will have a positive effect on plant growth depending on a particular plant’s UV requirements.
Solar Heat Gain
With the infrared-blocking capabilities of the Spectralight Infinity Tubing, removing greater than 50% of the heat from the IR wavelengths (>900 nanometers) of the sun with every reflection on the tube surface, the Solar Heat Gain of Solatube products is greatly reduced. This, in turn, will reduce the air conditioning load requirement for the space being daylit. These technologies allow Solatube Daylighting Systems to provide the highest light output performance with minimal thermal impact.
UV Effect on Skin and Vitamin D Production
The different UV wavelengths affect skin in the following ways.
UVA - The lowest energy range, UVA causes little burning ordinarily, but it penetrates deeply, beyond the surface layer of the skin. Over long periods of exposure, UVA causes wrinkling and premature aging of the skin.
UVB - More energetic, the chief burning and tanning rays which area major factor in producing skin cancer, although not penetrating beyond the skin.
UVC - The most energetic, intensely burning rays. Fortunately, UVC is mostly absorbed by the ozone layer, which essentially serves as “sunscreen” for the Earth.
Vitamin D production occurs when a compound within the skin reacts with UV rays between the 270-300 nanometers wavelengths, with peak synthesis between 295-297 nanometers. Based on this information the Solatube Daylighting Systems do not transfer the required UV for Vitamin D synthesis because it will block all of the UVB and UVC rays, which fall between the 100-315 nanometer range.
Note: The UV information in this article is specific to Solatube Daylighting Systems. Other TDD products may not provide the same performance standards.
Solatube® Daylighting Systems vary in price based on a number of factors, including:
- System model
- Roof type and pitch
- Tube length and angles
- Optional accessories and add-ons, such as Daylight Dimmers and tubing extensions
- Regional economy and location
Installation costs are listed separately, and vary based on region as well as the complexity and difficulty of the install. Your local Solatube daylighting expert can provide you with a free assessment and estimate. Call 1-888-SOLATUBE or request a quote here.