How Skylights Work

­Skylights typically are constructed with either plastic or glass, and the choice you make depends on several factors, including climate, location within the home and pricing. Manufacturers refer to types of skylights by their glazing, a general term used to describe how a skylight or window is constructed.

Plastic glazing for skylights is less expensive than glass glazing and yet it's still fairly durable. Plastic is more susceptible to wear, however, and will scratch, discolor or warp easily. And unless the plastic is coated with a special film, these kinds of glazes let in dangerous ultraviolet (UV) rays from the sun, which can harm people's skin and fade furniture, too. If you've ever seen dome- or bubble-shaped skylights in someone's home, chances are those skylights are ­plastic.Generally that design is considered out of style now.

Glass glazing for skylights is more expensive than plastic, but it's generally preferred because it's more durable than plastic, it doesn't discolor and many people simply think it looks nicer. Glass made for skylights must be made of safety glazing material, which means it has either been tempered or laminated. Tempered glass is glass that has undergone a process of heating and rapid cooling to make the material much harder than normal glass. As a result, when it breaks it shatters into small pebble-like pieces with no sharp edges. Laminated glass is made with a thin layer of plastic sandwiched between two pieces of glass. Although there are many different combinations, most manufacturers build skylights using a pane of tempered glass on the outside and a pane of laminated glass on the inside.

Various glazing techniques can increase a home's energy efficiency, too. Tinted glass can absorb heat and reduce the solar heat gain coefficient (SHGC), a measure of the amount of heat from sunlight a window or skylight blocks. How high or low you want your windows' SHGC depends on the climate in which you live -- the lower the number, the less heat is transmitted into your house. A skylight with a high SHGC, for instance, would be best to have for colder winters, while a skylight with a low SHGC is better at blocking heat during hot summers.

There are also low-emissivity (low-E) coatings on skylights, microscopically thin layers of metal spread over one or more of a skylight's panes. A low-E coating reduces the U-factor of a skylight -- the amount of non-solar heat allowed in. The lower the U-factor, the more efficient the window.

­People typically install skylights in bathrooms and kitchens in their homes. A skylight in the bathroom gives the room more natural sunlight, yet still maintains the privacy of the area. People tend to spend a lot of time in their kitchens, cooking and eating, so bathing this room in natural light is a nice way to spend mornings, afternoons or early evenings.

Whenever it's necessary to work around skylights, people need to pay extra attention to prevent any kind of fall accidents. A skylight accident can result in a long fall, which is bad enough, but there's also the added danger of broken shards of glass or plastic. There are as many as 36 fatal falls through skylights each year and as many as 50 nonfatal falls, the majority of which occur in construction jobs [source: USGlass News Network].

To minimize falls through these roof openings, the American Architectural Manufacturer's Association (AAMA) has provided several suggestions for safety around skylights. For one, anyone going up onto a roof, especially in the instance of construction, should be a professional who is properly trained in roof safety. Most accidents aren't caused by someone simply stepping through a skylight. According to the AAMA, other roof hazards -- such as uncovered openings -- are often to blame.. There should also be proper warning signs on and around the skylights when anyone is up on the roof.

For extra protection, homeowners and office building managers can install a skylight screen or railing over the skylights, which co­vers any glass or plastic and offers additional protection from accidental falls. They typically come in several different model types and sizes and fasten to or clamp down over the skylight. Most screens are dome-shaped and meant to fit over bubble-shaped plastic skylights, but some are flat and won't allow room for a skylight to open (if, of course, it's designed to open in the first place). Railings on the other hand, are much more prominent but are an obvious obstruction for anyone walking around on the roof.

For more illuminating information on skylights and related topics, take a look at the links on the next page.