The Benefits of Natural Light

Overview

Written by daylighting researcher Kevin Van Den Wymelenberg for the January/February 2014 issue of Architectural Lighting (posted online March 19, 2014), this technology feature asks what the research actually supports when designers claim daylight improves building performance and human health. It walks through the energy, financial, productivity and circadian evidence, is candid about where the science is thin, and closes with practical guidance for getting daylighting right.

Key Findings

• Electric lighting uses more than 15% of all electricity generated in the United States, and studies of daylight-sensing controls report lighting-energy reductions of 20% to 60%. Field results vary widely, from beating predictions by 56% to net increases caused by dimming-ballast behavior or lights left on after hours.
• Citing the Lighting Research Center's 2003 review, the author notes that windowless commercial space leases for about 20% less, or $2 to $4 per square foot below comparable windowed space.
• Heschong Mahone Group's retail studies found skylights were the third most important of five statistically significant drivers of sales volume, behind hours of operation and years since the last remodel.
• Ulrich's 1984 study found surgical patients with a view of trees recovered 8.5% faster and used fewer painkillers than patients facing a brick wall.
• HMG's 1999 school study linked daylit classrooms to test-score gains upward of 10%; a 2003 follow-up could not replicate the size of the effect but still found that a good view supports learning.
• In the author's own doctoral research, occupants who described glare as merely "just uncomfortable" reported a 10% drop in their perceived productivity.
• The circadian system responds most to short-wavelength light between 446 and 477 nanometers; without regular light-dark cues the sleep-wake cycle can drift up to two hours a day, and students deprived of morning blue light showed melatonin onset delayed by about 30 minutes.

Why It Matters for Daylighting

Two threads in this article map directly onto toplighting. First, the retail evidence the author leans on is specifically about skylights, not windows, and the sales effect appeared in big-box stores whose layout resembles a warehouse more than an office. Second, his three requirements for a successful installation, keeping direct sun off task areas during all occupied hours, balancing luminance across interior surfaces, and supplying enough ambient daylight for the work, are the design brief for a diffusing prismatic skylight. The glare finding cuts the other way: a clear skylight that throws a moving sunpatch across a picking aisle can erase the productivity benefit it was meant to create.

The author also flags the thermal side of the equation. Daylight glazing can raise or lower total energy use depending on how it is specified and operated, which is why skylight-to-floor ratios, U-factor and solar heat gain coefficient are governed by energy codes rather than left to taste.

About the Source

Architectural Lighting was the leading U.S. trade magazine for lighting design from 1986 until it was folded into Architect, which now hosts its archive. Kevin Van Den Wymelenberg was at the time an associate professor at the University of Idaho, director of its Integrated Design Lab and chair of the IES Daylight Metrics committee; he later moved to the University of Oregon. The library copy is an eight-page printout of the online article, which includes a short annotated list of daylighting resources. The original article is available on architectmagazine.com.