SATURDAY, Feb. 10 (HealthScout)—If you want Johnny to learn to read, let the sun shine in.

That's the advice of a growing number of educators, energy experts, and health-care providers who say that an abundance of natural lighting in classrooms creates a more healthful environment and also aids academic achievement.

Shedding light on this topic is timely because half the nation's 91,000 elementary and high schools are more than 40 years old and in need of major repairs or replacement, according to U.S. Department of Education statistics. At the same time, the student population, now at 48 million, is projected to grow to 54 million in the next nine years, says John Lyons, the educational facilities program manager for the Education Department.

So as school districts face critical choices in spending funds for maintenance, repairs and construction, Lyons adds, they need to understand how classroom environments—especially lighting—affect health and academic achievement.

The impact of daylight is well known for one particular effect. Most experts agree that as the hours of daylight grow shorter, particularly in northern climates, some people develop depression, irritability and fatigue—a triad of symptoms known as seasonal affective disorder, or SAD. The cause, experts believe, is an alteration of chemicals and hormones in the brain.

But, in what may be the most far-reaching finding of its kind so far, a three-state study found that daylight can also make a definite impact when it comes to classroom study and academic achievement.

The Heschong Mahone Group, an energy consulting firm in Sacramento, Calif., focused on 21,000 second-through fifth-graders in three elementary school districts in Orange County, California; Seattle, Washington; and Fort Collins, Colorado. The company's study used elementary-school classes because of the highly standardized test data available at that level of schooling and also because elementary students usually stay with one teacher in one class for most of their school day.

Using student test results from the three districts, the firm evaluated the natural-light conditions in more than 2,000 classrooms and found that overall, students in classrooms with abundant natural light had better math and reading scores than students in darker classrooms.

The school district with the most diverse light conditions, for example, also had the most striking test scores.

Lighting the Way

In Capistrano, which is in Orange County, California, the researchers found that students with the most daylight in their classrooms progressed 20 percent faster on math tests and 26 percent faster on reading tests in one year than those in the darkest classrooms. Similarly, students with the largest window areas did 15 percent better in math and 23 percent better in reading than those in rooms with the least window area. And in classrooms where a skylight diffused the daylight throughout the room, students improved 19 percent to 20 percent faster than those in classrooms without skylights.

The studies in Washington and Colorado also showed that students in classrooms with abundant natural light scored between 7 percent and 18 percent higher than those in dark classrooms, and that scores were higher in classrooms where teachers could control the amount of daylight and open the windows.