Is it time to develop fenestration daylighting ratings?

Daylighting gets a lot of attention in green building circles these days,and deservingly so. Studies have shown that increased daylighting levels provide benefits such as reduced absenteeism in schools, increased worker productivity, faster healing in hospitals, increased spending in stores, and more. Who doesn’t desire an office with a window; or even greater – the corner office? We all would rather read the morning paper under the light of day, than the harsh light of fluorescence. There is even a proven mood change due to the lack of natural light: Seasonal Affective Disorder. 

Of course, many of these benefits cannot be measured. The one attribute that can be quantified is energy savings. Providing independent and accurate daylighting ratings would offer a more complete picture of fenestration’s role in buildings, particularly its effect on reducing electricity consumption associated with indoor lighting.

NFRC’s Daylighting Rating Task Group held its first in-person meeting last fall in San Francisco. The task group’s scope is to create a rating system for daylighting potential using the existing NFRC visible transmittance rating combined with known, bright day incident illuminance values. The task group formed a working group to explore bright sky illuminance and to determine the best way to begin developing a rating.

The working group’s first assignment is to determine the type of sky needed to use in developing the rating, i.e., clear or diffuse. The working group is expected to present its recommendations at NFRC’s Spring 2011 Committee Week in Las Vegas, which will take place March 28-30.

The daylighting rating effort is in a preliminary stage. At this time, NFRC is exploring how to proceed. If NFRC pursues daylighting ratings, we will need to decide whether to create a complex model that takes into account the angle of the sun, orientation of the building, and other factors, or a simpler method that measures daylighting potential. Then, decisions would need to be made about whether to use an index or letter rating system, whether to integrate it with visible transmittance, etc.

It can take years to develop new rating procedures, and it requires the input of all interested stakeholders to ensure those procedures will be independent and credible. We invite you to learn more about NFRC’s exploration of daylighting ratings and to participate in the process.

--Jim Benney is the National Fenestration Rating Council’s chief executive officer. He has been involved in developing product and performance standards for the window and glass industry for more than 25 years. He can be reached at

The opinions expressed here are those of the individual author and do not necessarily reflect those of the National Glass Association, Glass Magazine editors, or other glassblog contributors.


Best to finish one task before starting another.....

I think the automotive industry has done a lot of work on this.   Is there a DOT standard that relates?   I was thinking about when Solex was developed to reduce heat gain.    Then there was some work done on applied films.    Maybe the beginnings of a standard already exist.  

As you consider the issue of a National Fenestration Rating Council (NFRC) daylighting rating and respond to the National Glass Association (NGA) weekly survey, please keep in mind that every NFRC rating and/or certification adds cost to the fenestration contract.  I can't help but wonder if the money would be better spent on today's product technology in the form of advanced low-emissivity coatings, dynamic glazing, and warm-edge spacers in lieu of the bureaucracy of NFRC?

It would seem that a rating sytem that can account for all the variations involved in efficient daylighting would be very cumbersome.  Consider the following: glass substrates, glass coatings, silkscreen coverages, curtainwall modules, sunscreen variations, light shelves, building orientation, climate, etc, etc..  How do you get all this into a relatively easy to use rating system? Individual building modeling (perhaps BIM) would seem to be a better, more cost efficient method. 

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