Shedding Light on the State of Daylighting

When it comes to optimal daylighting, a one-size-fits-all approach just doesn’t cut it. According to one expert on the topic, the design community continues to gain a better understanding of this, and the glazing and fenestration industries are eager to provide solutions.

That was the message from Dr. Neall Digert, vice president of product enterprise for Solatube International, Tuesday. He led a webinar sponsored by the American Architectural Manufacturers Association on the role of daylighting in codes, advanced building design and daylighting strategies.

Slide courtesy of Dr. Neall Digert of Solatube (via AAMA webinar)

Slide courtesy of Dr. Neall Digert of Solatube (via AAMA webinar)

“Daylighting is universally understood as one of if not the most important aspect of sustainable design,” said Digert. “… Sustainability not only looks at energy efficiency but also takes into account how design solutions nurture the building occupants.”

Because of the way the human body reacts to the spectral content of light and the way daylight helps regulate its natural cycles, “people are healthier, happier and more mentally engaged” when in naturally-lit environments, he said. He added that “occupants, not the building, drive annual performance” due to their resulting activity of their comfort level.

With that understanding, optimal daylighting must be achieved by mixing and matching fenestration systems while working within the constraints of energy codes.

Digert noted the shortcomings of designing only to prescriptive requirements. He pointed out that daylighting strategies of sidelighting (windows) and toplighting (skylights), as well as other “optically complex” systems each have benefits and limitations.

“One-size-fits-all prescriptive requirements rarely meet all our modern design needs,” he said.

He went on to discuss how the measurement of daylighting has evolved, particularly in ratings systems. For example, the first few versions of LEED maintained a “single point in time” design condition in referencing daylight.

LEED v4, however, adopted changes in how performance is determined, namely shifting from point-in-time analysis to “annual dynamic modeling.” It features new daylighting metrics including Spatial Daylight Autonomy and Annual Sunlight Exposure.

This, Digert said, tells much more of the story when evaluating the daylighting system’s performance.

Additional dynamic ratings and data have been developed, including Annual Visible Transmittance (VT annual), which accounts for how a product collects and transmits light to the building during the course of the year.

“VT annual provides much more meaningful inclinations for the designer,” he said.

He also discussed Net Zero energy requirements and the importance daylighting plays in meeting those goals. The need to not only reduce energy consumption but to also generate enough energy to reach that point poses an interesting dynamic. “You start to have a competition between the fenestration area and the photovoltaic area,” he said.

During the question and answer portion, he was asked about how glare is assessed and measured.

“The industry is working to try to address that,” he said. “It’s difficult. Currently, we’re most frequently looking at distribution of illuminance. … Glare metrics are still under development, and they’re a very hot topic among the industry.”

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