Skylights can add natural light to rooms that might otherwise have seemed dark and dreary, and can reduce the need for artificial lighting during the day. Inefficient or improperly installed skylights can also add to your heating and cooling costs.

The same factors that are important in energy-efficient windows are even more important in skylights. These include double-paned glazing with low-E coatings that reduce heat transfer. To find energy-efficient skylights, look for designs that meet the ENERGY STAR® guidelines.

Skylights can be made of either glass or plastic glazing. Double glazed low-e glass has the best resistance to heat transfer. Plastics can be molded into a variety of shapes, and one-piece molded skylights are good choices to avoid air leakage. Plastics do tend to deteriorate from prolonged exposure to sunlight.

Heat loss through skylights on horizontal or steeply slanted roofs is significantly higher than through equivalent windows on horizontal walls. One reason for this, particularly with poorly insulated skylights, is that, when it's cold, the cold air from the skylight tends to set up a convection loop. Warm air rises, hits the skylight, is cooled and then falls down to be warmed and repeats the cycle. This can create drafts and increase heating costs.

One fairly energy-efficient and inexpensive way to bring natural light into your home is tubular skylights. These are skylights that have a small clear acrylic dome on the roof and a tube with a highly reflective interior that helps maximize the amount of natural light entering the house. A diffuser helps spread the light throughout the room. The tube is sealed and only a small roof opening is required, both of which help minimize the amount of heat loss and heat gain. Some tubular skylights include electric lights so the fixture can provide light both day and night.

The direction a skylight faces is an important factor in the amount of light and heat the skylight lets in. Skylights that face south and west can allow excessive heat gain in the summer. The slope of the skylight also affects solar heat gain. A lower slope admits relatively more solar heat during the summer and less in the winter. The optimum slope in North Georgia is 38 to 49 degrees.

You can prevent excessive solar heat gain by installing the skylight in the shade of trees that lose their leaves in the fall or by installing some type of movable shading. One option is motorized remote-controlled blinds.

It's very important that skylights are correctly installed, with adequate flashing and caulking, to prevent air and water leaks through spaces between the frames and glazing. Always follow the manufacturer's installation guidelines. Before hiring a professional installer, be sure to get several estimates and check references.

For more information about energy-efficient glazing, see the Web site of the Efficient Windows Collaborative at www.efficientwindows.org.