Measure 8.3.1 Install skylights or light pipes.

Where to Use Skylights and Light Pipes
Energy Saving Potential
Surface Area Required for Daylighting
Skylight Layout
Effective Diffusion is Essential
Avoid Nasty Surprises: Heat Loss and Condensation
Skylight Materials
Skylight Configurations
How to Prevent Water Leakage
Control Electric Lights
Compatible Types of Electric Lights
Special Features of Light Pipes
Economics
Traps and Tricks

Skylights can provide satisfactory lighting for activities that can tolerate large variations in illumination level. Getting good performance from skylights is not as simple as it may appear. You have to satisfy a number of requirements, some of which may not be easily compatible with each other.

When considering skylights, also consider “light pipes.” Light pipes perform the same function as skylights. They make it possible to transport daylight through thick roof structures and attics. They are easier to install in retrofit applications than skylights. For practical reasons, light pipes are limited to smaller light collection areas. They are still evolving.

In this Measure, we will use the term “skylights” to cover both skylights and light pipes, except when the distinction needs to be spelled out.

Where to Use Skylights and Light Pipes

Many types of activities can be illuminated well by skylights, but many others cannot be. In terms of illumination quality, the major advantage of skylights is the ideal color rendition of daylight. Their major disadvantage is large fluctuations in illumination intensity caused by movement of clouds across the sun. This annoyance varies with location.

Experience indicates that skylights can be effective for retailing, even in posh environments, because sunlight has excellent color rendition and brilliance. See Figures 1, 2, and 3.

Skylights are also effective for many manufacturing and maintenance operations. Warehousing can be a favorable application. Skylights can be used to provide a sense of natural ambience, which is valuable in applications such as restaurants (Figure 4), transportation centers, and other public areas.

Skylights are less likely to be satisfactory where paperwork occurs, as in offices, drafting areas, and reading rooms. The wide range and fluctuations of sunlight intensity are more noticeable in applications that require concentration on text. Also, daylighting makes it more difficult to avoid veiling reflections, which are a problem especially with paperwork. See Reference Note 51, Factors in Visual Quality, for more about veiling reflections.

With current technology, skylights and light pipes are limited to illuminating the area directly underneath them. The roof structure must allow penetrations to be made without undue expense. Therefore, skylights are most likely to be worthwhile in industrial-type buildings

Fig. 1 Effective skylights in a shopping mall The percentage of ceiling area is about right for the type of illumination needed. Light distribution is good. The diffusing skylights are installed at the tops of tapered recesses, minimizing glare.

and in large single-floor spaces, such as gymnasiums. Future types of light pipes may be able to transport sunlight far into the building interior.

Skylights must be located where the sun can shine on them directly. A skylight does not produce a useful amount of daylight if it is shaded by adjacent structures or foliage. Similarly, skylights are not worthwhile in areas that have heavy cloud cover for a large fraction of the time, unless the climate is mild and the structure can accommodate a large area of skylights. Clouds typically reduce solar illumination by a factor of five to ten.

When individual clouds pass in front of the sun, they cause abrupt changes in illumination level. The abruptness of the change is usually more objectionable than the reduction of light level. The large, quick variations of light level make skylights unacceptable for certain applications.

Retrofitting skylights in existing buildings is often impractical because of cost and structural interference. Even though skylights require only a relative small fraction of total roof area, installation usually requires structural changes, such as cutting through rafters and purlins.

If the building has an attic, installing skylights in the roof requires building a reflective enclosure to pass the light through the attic. Unless the attic is empty, this may be difficult. Light pipes are easier to pass through attics. In effect, a light pipe is a small skylight with an integral reflective enclosure.

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These excerpts shows the level of detail and accuracy that you'll find in the Energy Efficiency Manual by Donald Wulfinghoff. This 1500-page manual offers the most comprehensive coverage of energy-saving measures for buildings ever assembled under one cover. For more information and to view the complete table of contents, find the Energy Efficiency Manual in the Oikos Bookstore.