Daylighting and Productivity

By Kenneth J. Cooper
Washington Post Staff Writer
Friday, November 26, 1999; Page A14

Click here to view the article posted on the Sacramento Bee website

By Carrie Peyton,  Bee Staff Writer 
(Copyright Sacramento Bee, published June 28, 1999)

Can a few beams of sunshine help lessons soak in?

A new study, one of the largest ever done on natural light in schools, suggests children learn faster and do better on standardized tests in classrooms with more daylight.

Learning rates were 26 percent higher in reading and 20 percent higher in math in rooms with the most natural light, researchers found.

A companion study found that sales were 40 percent higher in stores with skylights, compared with almost identical stores in the same chain without skylights.

Psychologists and energy efficiency experts alike have long suspected that something as simple as sunshine may help people work more efficiently, learn more, call in sick less often and sell more.

The research, conducted by a Fair Oaks energy consulting firm for the state Board for Energy Efficiency and Pacific Gas and Electric Co., is one of the largest and most rigorous attempts to test those suspicions.

"My guess is this will make a huge impact on school design in the next few years," said Arthur Rosenfeld, a senior adviser for energy efficiency for the U.S. Energy Department.

While stressing he hadn't yet read the studies, Rosenfeld described the review team that evaluated them as "a star group," and said their level of certainty is "very, very impressive."

Rosenfeld heads a subcommittee of the National Science and Technology Council that will be reviewing hundreds of reports on the issue this summer, in an effort to separate hunches from evidence.

"Until fairly recently, the papers just haven't been convincing," he said.

What tidbits there were, were tantalizing.

A Wal-Mart store improved sales in areas lit by skylights, no matter what merchandise it put there. Wal-Mart never released any statistics for researchers to analyze, but within the past year it decided to build all its new stores with more natural light. Costco and HomeBase both have begun designing new stores with skylights, and Target has been studying their effect on energy use and sales.

"In retail there's been much more attention to this because of the economics," said Judith Heerwagen, a Seattle environmental psychologist who helped review the school data gathered by Fair Oaks architect Lisa Heschong.

"It's absolutely intriguing work," Heerwagen said. "Her results were pretty consistent across the sites, which suggests there clearly is something going on here."

The Heschong-Mahone Group brought in statisticians to analyze test scores of more than 21,000 elementary school students in three Western school districts.

In the Capistrano Unified School District in Orange County, where children were tested at the beginning and end of each school year, a comparison of 750 classrooms showed more improvement in those with the most daylight.

In those classrooms, students scored 2.3 points higher in reading and 2.5 points higher in math than students in the rooms with the least daylight.

Over the course of the school year, in all lighting situations, the district's students on average increased their scores 8.8 points in reading and 12.5 points in math.

In the Seattle Public School District, where students were tested only once a year, those in rooms with the most daylight had 13 percent higher reading scores and 9 percent higher math scores than those in the least. Similar testing in Fort Collins, Colo., showed 7 percent higher scores in reading and math.

Heschong said she didn't know what might be causing the effect.

"Daylight is a very complex thing. It affects how we see, and it also affects us biochemically" in ways that alter alertness, she said.

People also just plain like windows.

"I know I work better when things are open and bright," said teacher Kelly Baker.

She said her fourth-graders seemed more attentive and better focused after they moved from a nearly windowless portable to a bright, newly remodeled classroom at John Holst Elementary School in Fair Oaks.

The workplace preference for windows is so strong that in Europe, "you're not allowed not to have access to daylight. It's considered inhumane," said Eleanor Lee, a specialist in building technologies at the Lawrence Berkeley National Laboratory.

The new daylight research, detailed in twin reports finalized last week, is "one of the better recent studies that indicates there are effects here worth looking at," said Steve Selkowitz, who coordinated the scholarly review of the findings.

"People have tried to study it on a smaller scale, but doing it on a larger scale with more data sets is important," he said.

Selkowitz, head of the building technologies department of the Environmental Energy Technologies Division at the Lawrence Berkeley lab, cautioned that there is "a complicated set of pathways between a cause and an effect."

Virtually everyone, he said, would agree that "the single most important parameter affecting student scores is the teacher."

Steve Looper, a computer teacher at James McKee Elementary in Elk Grove, said he has worked in a range of classrooms and never seen a daylight effect.

"There are a lot of other factors that would improve student performance a whole lot more," he said, such as "getting kids to have enough sleep the night before or to have breakfast in the morning."

Still, those interested in energy savings from the building technique called "daylighting" are expecting more research as fascination with the subject continues to grow.

Interested parties include utilities, which have long advocated buildings that use skylights, well-placed windows, reflecting surfaces and other designs that let people conserve energy by turning off electric lights.

The Sacramento Municipal Utility District's light-drenched customer service center saves SMUD the equivalent of about $56,000 a year in electric bills, an independent study found.

While the energy conserved by daylighting makes a big difference, nationwide, that's not as exciting to builders or building owners as its effects on people inside, said Selkowitz.

"Very generally, if you look at costs in very round numbers, energy costs about $2 per square foot per year, and people cost about $200 per square foot" in an office building.

So even a tiny improvement in productivity or sick time will pay off far more quickly than energy savings, he said.

This study looks at the effect of daylighting on human performance. It includes a focus on skylighting as a way to isolate daylight as an illumination source, and separate illumination effects from other qualities associated with daylighting from windows. In this project, we established a statistically compelling connection between daylighting and student performance, and between skylighting and retail sales. This report focuses on the school analysis.

We obtained student performance data from three elementary school districts and looked for a correlation to the amount of daylight provided by each student’s classroom environment. We used data from second through fifth grade students in elementary schools because there is extensive data available from highly standardized tests administered to these students, and because elementary school students are generally assigned to one teacher in one classroom for the school year. Thus, we reasoned that if the physical environment does indeed have an effect on student performance, we would be mostly likely to be able to establish such a correlation by looking at the performance of elementary school students.

We analyzed test score results for over 21,000 student records from the three districts, located in Orange Country, California, Seattle, Washington, and Fort Collins, Colorado. The data sets included information about student demographic characteristics and participation in special school programs. We reviewed architectural plans, aerial photographs and maintenance records and visited a sample of the schools in each district to classify the daylighting conditions in over 2000 classrooms. Each classroom was assigned a series of codes on a simple 0-5 scale indicating the size and tint of its windows, the presence and type of any skylighting, and the overall amount of daylight expected.

The study used multivariate linear regression analysis to control for other influences on student performance. Regressions were compared using data from two separate tests, math and reading, for each district. Each math and reading model was also run separately using first the window and skylight codes, and then the overall daylight code. We reasoned that if daylight effects were truly robust the variables should perform similarly in all models. Thus, we created a total of twelve models for comparison, consisting of four models for each of three districts.

The daylighting conditions at the Capistrano school district were the most diverse, and the data from that district were also the most detailed. Thus Capistrano became our most precise model. In this district, we were able to study the change in student test scores over a school year. Controlling for all other influences, we found that students with the most daylighting in their classrooms progressed 20% faster on math tests and 26% on reading tests in one year than those with the least. Similarly, students with the largest window areas were found to progress15% faster in math and 23% faster in reading than those with the least. And students that had a well-designed skylight in their room, one that diffused the daylight throughout the room and which allowed teachers to control the amount of daylight entering the room, also improved by 19-20% faster than those students without a skylight. We also identified another window-related effect, in that students in classrooms where windows could be opened were found to progress 7-8% faster than those with fixed windows, regardless of whether they also had air conditioning. These effects were all observed with 99% statistical certainty.

The studies in Seattle and Fort Collins used the final scores on math and reading tests at the end of the school year, rather than the amount of change from the beginning of the year. In both of these districts we also found positive, and highly significant, effects for daylighting. Students in classrooms with the most daylighting were found to have 7% to 18% higher scores than those with the least.

The three districts have different curriculum and teaching styles, different school building designs and very different climates. And yet the results of studies show consistently positive and highly significant effects. This consistency persuasively argues that there is a valid and predictable effect of daylighting on student performance.

This study looks at the effect of daylighting on human performance. It specifically focuses on skylighting as a way to isolate daylight as an illumination source, and avoid all of the other qualities associated with daylighting from windows. In this project, we established a statistically compelling connection between skylighting and retail sales, and between daylighting and student performance. This report focuses on the retail analysis.

We analyzed data on the sales performance of a chain retailer who operates a set of nearly identical stores. The analysis included 108 stores, where two thirds of the stores have skylighting and one third do not. The design and operation of all the store sites is remarkably uniform, with the exception of the presence of skylights in some. The electric lighting was primarily fluorescent. The skylights often provided far more illumination, often two to three times the target illumination levels. Photo-sensor controls turned off some of the fluorescent lights when daylight levels exceeded target illumination.

The monthly gross sales per store were averaged over an 18-month period that went from February 1 of one year to August 31 of the following year. This average sales figure was transformed into a "sales index" that we could manipulate statistically, but that did not reveal actual dollar performance. Stores in the sample were selected to operate within a limited geographic region that had similar climatic conditions, and to have a constrained range of size and age. The geographic region has a relatively sunny climate. All of the stores in the data set are one story.

The multivariate regression analysis allowed us to control for the influence of other variables, which might influence sales. Other variables considered included the size and age of the store, hours of operation, and economic characteristics associated with the zip code location.

Skylights were found to be positively and significantly correlated to higher sales. All other things being equal, an average non-skylit store in the chain would be likely to have 40% higher sales with the addition of skylights, with a probable range somewhere between 31% to 49%. This was found with 99% statistical certainty. After the number of hours open per week, the presence of skylights was the best predictor of the sales per store of all the variables that we considered. Thus, if a typical non-skylit store were averaging sales of $2/sf, then its sales might be expected to increase to somewhere between $2.61 to $2.98 with the addition of a skylighting system.