CONTROLLING HEAT GAIN FROM SKYLIGHTS
Skylights shades come in two types: exterior and interior. As an example of the former, “HeatBlocker Shades,” made of durable fabric with a perimeter elastic band, are applied like a shower cap over acrylic dome-shaped skylights. Typically, these shades are put on in the summer and removed in the winter when maximum light (and even some solar heat gain) is desirable.
The drawback to most exterior skylight shades, however, is the lack of control in regulating the sunlight — the device is either on or it’s off. By contrast, interior shades, which can be opened and closed at will, are more versatile: in your bedroom they allow you to sleep in on a bright summer morning, or in a family room they prevent daytime TV viewing from being impaired by the sun’s glare on the screen. The fabric of interior skylight shades ranges from very sheer (when the goal is simply to “soften” the light) to “room darkening.” In situations where the shade is within reach of a control rod, manual operation works fine. However for skylights installed in high places, most homeowners choose electric shades, which are opened and closed with the touch of a wall switch or remote control. Battery and solar-powered devices are now available aswell, eliminating the hassle of running wires above the ceiling.
As an alternative to shading, the principle of reflection can also be used to control heat gain from skylights. White acrylic domes are the most obvious example of this. If you have a clear or bronze-tinted skylight, changing out the plastic to white will generally cut down on heat gain by reflecting a good portion of the sun’s heat. Reflection is also at work in Low E glass. The “spectral selectivity” of this type of glazing blocks the longer wavelengths that make up the heat portion of the electromagnetic spectrum while letting in the shorter wavelengths that appear in the form of visible light. Thus, replacing energy-inefficient acrylic skylights with Low E glass units provides the best of both worlds: maximum illumination with minimal warming effect.
