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Light Pipes Often Fit Where Skylights Can’t

Fri., April 12, 1996

Q. At a recent home and garden show I saw several displays of light pipes an alternative to skylights.

What can you tell me about them?

A. Like skylights, light pipes reduce the need for artificial lighting in the home. They are new on the market.

A light pipe consists of a metal tube, about one foot in diameter, that starts at the ceiling and extends to approximately one foot above the roof. A clear plastic dome covers the outside end and a translucent lens on the inside end defuses the incoming light.

Light pipes can bring natural light into an area too small for a skylight, such as a hallway or a closet. Another possibility might be a bathroom where a skylight could compromise privacy.

How much light do they bring into a room? Typically a light pipe can illuminate up to 400 square feet. There are currently six manufacturers of light pipes. One of these manufacturers asked the Alberta Research Council to test its brand of light pipe.

The council found that at noon on a sunny December day the 13-inch diameter light pipe transmitted light equivalent to a 700-watt incandescent bulb. In June, this same pipe transmitted light equivalent to a 1,200-watt bulb.

A similar set of tests of all major brands, done by the University of Calgary, found comparable results. These researchers found a four-foot light pipe transmitted 84 percent of the ambient light. A six-foot light pipe did almost as well, transmitting 73 percent of the light. The tests were done on both sunny and cloudy days. The tested light pipes transmitted as much as one-third less light on cloudy days. These figures are for the tubes only.

The upper dome and lower diffuser of a complete assembly reduce total transmission by about 50 percent. That still allows plenty of light to enter. There are also some differences between the various light pipes, depending upon the reflectivity of the inside pipe surface.

How much do light pipes cost to install? Installation costs typically run between $300 and $400. Residential models come in diameters of 10, 13 and 14 inches. This allows the pipe to fit between most rafter systems. Various tube or pipe lengths are also available. One manufacturer said company installers can do a normal installation in about two hours.

Accessories include color filters for the diffuser and a light scoop for the top that will help to gather more light during the winter months. One manufacturer offers oval-shaped ceiling diffusers for installations in a vaulted ceiling. These come to match the most common roof pitches. There are also roof jacks to meet these various pitches.

Light pipes have been used with good results in northern Canada during cold weather. The only problem encountered so far is a tendency for moisture to condense on the inside of the plastic dome during cold weather. An air permeable gasket may allow the light pipe to breathe, which will solve this problem. Also there will be a very small amount of heat lost up the tube, but not enough to be concerned about.

If you want to install a light pipe on your own, check with local building supply houses. For a list of manufacturers, call the Energy Hotline at 324-7980 or (800) 962-9731.

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