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Brighten Up With Daylighting

Daylighting is the use of direct, diffuse, or reflected sunlight to provide natural interior illumination. It is one aspect of passive solar design that can be incorporated easily and effectively anywhere in the U.S.

When properly incorporated, daylighting provides warmth and brightness while offering energy savings. The natural light provides visual relief, better contact with nature and time orientation. Daylighting also results in energy savings by lowering the use of electric lights, a significant component of internal heat gain, thereby reducing the the home's required air conditioning capacity and use. In contrast, when not properly designed, the natural sunlight can cause annoying glare any time of year, and send your air conditioning bills soaring in the summer.

In single family homes daylighting is usually provided by windows, skylights and clerestory windows (vertical windows located high on an interior wall). Larger buildings sometimes also use light shelves: horizontal light-reflecting overhangs placed above eye-level, which reflect light through transom or clerestory windows placed above.

Design Tips for Daylighting

Natural lighting comes from three sources:

Generally, light that comes from above causes less glare. That is why ceilings should usually be more relective than walls, and why clerestory windows are such a good souce of daylighting. Raising the top height of a window will result in deeper penetration and more even illumination in the room. Punched window openings, such as small, square windows separated by wall area, result in uneven illumination and harsh contrast between the window and adjacent wall surfaces. A more even distribution is achieved with horizontal strip windows

Direct, unfiltered sunlight also causes glare, so take care when using larger windows, or when adding skylights. Tubular skylights are an excellent source of low heat, indirect daylighting. They guide the sunlight to a diffuser lens mounted on the interior ceiling surface that spreads light evenly throughout the room

Highly reflective interior surfaces will better bounce the daylight around the room, spreading the light and reducing extreme brightness contrast. High reflectance paints and ceiling tiles are now available with 90% or higher reflectances, and can be purchased at almost any paint store. Just check the label on the paint can. The Department of Energy's daylighting design guidelines suggest that walls should have reflectances of 50 to 70 percent, and ceilings should have reflectances of 90 percent or more. Window frame materials should be light-colored to reflect more light into the room and to reduce contrast with the view outside.

To take full advantage of the energy-savings potential of daylighting, make sure that window overhangs are properly sized to allow sunlight into the house during the heating season and to shade the windows during the cooling season.

There are simple ways to enhance your use of existing daylight through careful interior design. Desks, reading chairs, and dining room tables can be strategically located to best use the available light. But beware of glare problems if locating a computer in a daylit area.

Other Resources

The Durability Checklist from Durability by Design - A Guide for Residential Builders and Designers includes several items that support effective use of daylighting.

Always check ENERGY STAR's recommendations when selecting windows and skylights.

The Lawrence Berkeley National Laboratory provides more detailed tips and guidelines for daylighting.

Content updated on 8/3/2006

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