Let the sunshine in...but not too much

Daylighting strategies have become an accepted and expected part of school facility design. The benefits of daylighting appeal both to the educators responsible for teaching students and to the facility managers given the task of operating school buildings efficiently.

Educators have been won over by research that has shown that students in classrooms with well-designed daylighting strategies tend to perform better in reading and math than students in classrooms without well-designed daylighting. Facility managers see the benefits daylighting brings to their operating budgets—the more natural light that can be used to illuminate a building interior, the fewer dollars a school system will have to spend on the electricity that powers artificial lighting.

More is not necessarily better

If some daylight is good, then more daylight is better—right? Not if you’re trying to create an effective learning environment. Too much daylight, especially direct sunlight, can create glare that distracts students and makes it difficult to see work surfaces like a computer screen or a whiteboard.

The 1999 study of classrooms and daylighting by the Heschong Mahone Group, frequently cited as pivotal in persuading school designers to incorporate daylighting strategies, concluded that students in daylighted classrooms showed significant gains in math and reading performance. But those findings applied to well-designed daylighting—spaces where daylight is diffused and not allowed to enter directly. In fact, the study found that classrooms outfitted with skylights that allowed sunlight directly into the space had a negative effect on student performance.

Daylighting principles

The U.S. Department of Energy’s Best Practices Manual for Building High Performance Schools list six principles that form a foundation for effectively designing daylighted spaces.

•Prevent direct sunlight penetration into glare-sensitive teaching spaces.

“A carefully oriented building design will allow maximum daylight while minimizing unwanted solar gains,” the manual states.

It is easiest to provide excellent daylight conditions using north-facing windows, because the sun strikes a north-facing window only in early morning and late evening during midsummer. South-facing windows are the next best option because the high angle of the south sun can be easily shaded with a horizontal overhang. East- and west-facing windows are more problematic because when the sun is low in the sky, overhangs or other fixed shading devices are of limited utility.

•Provide gentle, uniform light throughout space. Evenly diffused daylight will provide the most energy savings and the best visual quality.

“It is easiest to achieve uniform daylight illumination from toplighting strategies that distribute light evenly across a large area,” the manual says. “The next best approach is to provide daylight from two sides of a space with a combination of view windows and high windows, preferably no more than 30 feet to 50 feet apart.”

•Avoid creating sources of glare.

“Eliminate glare by obscuring the view of bright sources and surfaces with blinds, louvers, overhangs, reflectors, and similar devices,” the manual says.

•Give teachers the ability to control daylight in a classroom with operable louvers or blinds.

Teachers should have easy access to controls for shades or blinds to adjust light levels as the amount of daylight changes throughout a day, the manual says.

•Design the electric lighting system to complement the daylighting design and encourage maximum energy savings through the use of lighting controls.

Electric lighting generates heat, so substituting daylight for electric lighting helps reduce cooling costs as well as lighting costs.

“But these energy savings will only be achieved if the electric lights are turned off or dimmed in response to the daylight,” the manual says. “The electric lighting should be circuited and controlled to coincide with the patterns of daylight in the space, so that the lights can be turned off in areas where daylight is abundant and left on where it is deficient.”

•Plan the layout of interior spaces to take advantage of daylight conditions.

In general, the manual says, work areas should be oriented so that daylighting is available from the side or above. Facing a window may introduce direct glare into the visual field, and facing away from a window may produce shadows or reflected glare.

Window types

The best practices manual also describes several types of windows used to incorporate daylighting into school spaces.

•View windows. Use view windows to provide exterior views for all interior spaces where students or staff will be working for extended periods of time.

•Clerestories. Use high clerestories in perimeter walls to increase daylight delivery deeper in classrooms, offices, libraries, multipurpose rooms, gymnasiums, and administrative areas.

•Clerestory with light shelf or louvers. Use light shelves or louvers with high clerestory glazing to improve daylight distribution; block direct sun penetration; and minimize glare in classrooms, offices, libraries, multipurpose rooms, gymnasiums, and administrative areas.

•Central toplighting. Central toplighting uses a central monitor or skylight (or cluster of skylights) to distribute daylight evenly across a room. Daylight is diffused with diffusing glazing or baffles.  In single-story classrooms central toplighting provides high levels of even, balanced daylight across an entire room.

•Patterned toplighting. It provides daylight through a two-dimensional grid of skylights or rows of linear monitors. This daylighting pattern is useful for any large area that needs even daylight levels,” the manual says. “It is especially good for gymnasium, library, multipurpose, or cafeteria spaces.”

•Tubular skylights. They are used for toplighting in areas with relatively deep roof cavities. They are small clear-domed skylights with mirrored reflective ducts connecting them to the ceiling plane of a space. They have an interior diffuser at the ceiling plane to spread daylight in the space.

“Tubular skylights are especially good for small spaces, such as toilet rooms, locker rooms, kitchens, interior corridors, enclosed staff work areas, and other interior spaces that are sporadically occupied and would benefit from a low-cost toplighting solution,” the manual says. “They are also good for retrofit into any existing school space that needs extra daylight or needs to balance an existing asymmetric daylight distribution.”