Top Five Tips for Successful Daylighting Design

Equip every project to meet its own unique performance goals
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Sponsored by Lutron Electronics
By Jeanette Fitzgerald Pitts

Tip #5: Select Specification-Grade Fabric

Unfortunately, new evidence has revealed that even if a specifier selects fabric with the properties that should manage daylight as desired, it is highly likely that a fabric with different properties will end up on the job site. Combat this industry-wide standardization problem with specification grade fabrics: fabrics that guarantee their delivered product will match the specified performance.

The Study

A recent manufacturer-led analysis tested more than 200 fabric samples from all of the major U.S. fabric suppliers in the industry. The test measured the openness factors and Tv values of the fabric, and compared the actual values with the values promoted on the fabric cards and other marketing materials. The deviation was astounding. Not only was a difference between the actual values and the listed values common, the difference was enough to materially affect the way that the shade would perform.

Deviation in Openness Factors

Openness factors with a margin of error of up to 3 percent were found. This means that if a fabric with an openness factor of 5 percent was specified, a fabric with an openness factor of between 2 and 8 percent could have been installed. Fabrics with openness factors that are higher than specified may expose a space to greater degrees of glare, while lower openness factors will compromise the available view.

Deviation in Tv Values

The study found fabrics where the actual Tv value was more than two times higher than the posted Tv value. This means that if a fabric with a Tv value of 7 percent was specified, it is possible that a fabric with a Tv value greater than 14 percent may have been delivered. This dramatic increase in Tv value could create a real diffuse glare problem, while significantly lower Tv values may limit the amount of energy savings able to be realized on a project.

The Solution: Specification-Grade Fabric

Specification-grade fabrics, or spec-grade fabrics, are fabrics that a manufacturer guarantees will meet the specified performance metrics. The purpose of these spec-grade fabrics is to give specifiers the confidence that the fabric delivered to the job site will meet their design intent. To that end, spec-grade fabrics adhere to rigorous manufacturing protocols, testing, and measurement standards, and are supported with meticulous documentation.

Good daylighting design is difficult. It requires the management of a dynamic and intense source of light and heat, the satisfaction of often conflicting project goals, and the ability to balance the need to allow daylight into a space, while preventing glare and solar heat gain. There are five tips for achieving successful daylighting on a project: 1) define and prioritize daylighting performance goals; 2) select interior solar shades; 3) choose automated control; 4) consider more than color when specifying a solar shade fabric; and 5) select specification-grade fabric. Applying these five tips to a daylighting project will not change the fact that good daylighting design is difficult, it just won’t be difficult for you.

End Notes

1 Future Workplace. (2018)

2 Heschong Mahone Group (2003). Windows and Offices: A Study of Office Worker Performance and the Indoor Environment. Detailed Report. Fair Oaks, CA.

3 Browning, B., Cooper, C. (2015). The global impact of biophilic design in the workplace. Interface. Retrieved from:


5 Farley, K. M., & Veitch, J. A. (2001). A room with a view: A review of the effects of windows on work and well-being.

Jeanette Fitzgerald Pitts has written dozens of continuing education articles for Architectural Record covering a wide range of building products and practices.


Lutron Electronics, headquartered in Coopersburg, Pennsylvania, designs and manufactures energy-saving light controls, automated window treatments, and appliance modules for both residential and commercial applications. Its innovative, intuitive products can be used to control everything from a single light to every light and shade in a home or commercial building.


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Originally published in Architectural Record
Originally published in October 2016