Tubular skylights (or solar pipes, sun pipes, light tubes, etc.) are an effective way to increase natural daylighting in you home. You may have seen these installed in hallways, bathrooms or closets in different homes.
There are many types on the market nowadays that incorporate features like light fixtures that turn on at dusk (using a photocell), or fans that kick in for ventilation using a temperature sensor. These skylights are an excellent example of light conservation and saving electricity, and prolonging the number of natural daylight hours.
How They Work
Fundamentally, the technology behind natural tube lights is pretty simple, inexpensive and constantly improving. Since they are usually dome-shaped for household applications, the diameters are sized to fit between roof rafters and ceiling wood joists, which means that there are no structural changes necessary to install them, as with skylights. This also means that the risk of leaks through the roof is decreased.
Tubular skylights are built using a clear acrylic dome that passes light through a super-reflective interior. A translucent dome then spreads diffused daylight throughout an area. One advantage of diffused light is the reduced damage to carpets and furniture due to lower ultraviolet radiation from the light. The other advantage is that there is no harsh glare from direct sunlight. (click here to read about the solar tubes in my house)
These devices are available in different diameters and pipe lengths for different light levels depending on daylight conditions. Tubular skylights also deliver a higher volume of light with no glare as compared with skylights (which deliver a shaft of light directly below the lightwell). According to tests performed at research labs such as Berkeley or Calgary, light tubes are effective in transmitting up to 90% of the entering light.
Because the rooftop solar collector has a small surface area and because of the airspace between the collector and the diffuser, building heat loss in the winter and heat gain in summer are minimized. Their small size also minimizes their impact on the home's appearance.
Tubular skylights generally do not encounter condensation problems. Also, because of the airspace between the collector (dome) and the diffuser, there is very little heat loss during the winter and heat gain in summer than skylights.
Tests performed at Alberta Research Council indicate the light output from a 13" Sun Lite-brand pipe at noon on a sunny day is equivalent to a 700-watt incandescent bulb in December and a 1,200-watt incandescent bulb in July. Keep in mind that these are tests conducted in ideal lab conditions.
I would equate the light from the light pipes in my home (in the northeastern part of the U.S.) to a fraction of these values. The variation is due to the location of the dome on the roof, the length of the reflective tube in the attic, the material the diffuser and the dome are made of, and the amount of shading over the dome.(click here to read about the solar tubes in MY house)
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