Shedding Light on LEED v4’s Daylight Credit

Considered to be the most significant overhaul of the U.S. Green Building Council’s LEED green building rating system since its inception, LEED v4 has officially raised the sustainable bar in its attempt to redefine what is considered to be a green building.

Along with some of the more impactful changes — such as more stringent energy and water efficiency requirements, and the incorporation of Life Cycle Assessment data in building product reporting — v4’s Daylight credit has been updated, incorporating new metrics.

In sync with advancements in daylighting modeling, spatial daylight autonomy (sDA) — which measures lighting levels by the percentage of the workplane that is brighter than 28 footcandles for at least half of the space’s occupied hours — is now the preferred metric.

Considered to be a more accurate assessment of quality daylighting, v4 offers more points for designs utilizing sDA, as compared to traditional illuminance calculations for specific points within a year-long cycle, which is still accepted by LEED v4.

A more sophisticated metric, sDA also takes into account average weather conditions, exterior obstructions and attached furniture systems. This includes calculating measurements with the application of blinds, operated hourly, to block direct sun rays predicted to enter the space.

While LEED v4 encourages the use of sDA, it is known that the metric has a tendency to create overglazing. In order to balance this out, architects are also expected to perform glare simulations on their designs, per LEED v4.

Another noted change in the rating system’s lighting requirements is the inclusion of ASHRAE 90.1-2010, mandating that maximum lighting power density is ramped down to an average of 17 percent, with the exception of automotive facilities, hospitals and hotels.

The upshot is that designers will be forced to use better daylight harvesting and lighting control strategies in order to accomplish this.

“From ASHRAE 90.1-2007 to ASHRAE 90.1-2010, there is approximately a 25% improvement in energy use/reduction,” explains Jeff Saad, associate principal, Perkins+Will, Chicago. “To achieve the increased standard, greater focus will have to be placed on systems working synergistically.”

Daylighting is an important issue for interior designers and facility managers and one that can be an important part of your marketing and communications program. Demonstrating your understanding of the issue and how your product supports proper daylighting will strengthen your position as a valued partner to specifiers, installers, designers and end-users.