by Edward Dean, AIA

The use of natural light in libraries has traditionally been understood as a desirable building feature and a hallmark of good library design. When skillfully introduced, daylight creates an ambience of quiet contemplation and visual comfort, and links the modern library user psychologically with the pretechnological past.

Daylighting design has recently taken on a new appreciation, beyond aesthetic and psychological aspects, with the advent of energy shortages and sustainability concerns. The alternative to daylighting, namely the use of electric power for library lighting, contributes to the strain on electric generation capacity as well as the inefficient use of nonrenewable energy resources.

Furthermore, the cost of lighting a library has become a major burden to communities and will continue to increase in the future. Daylight, which is free, provides the opportunity to reduce these negative impacts created by the over-dependence on electric lighting sources.

When sunlight enters the space through a window or skylight, it brings not only light energy (whether direct or indirect, but preferably indirect light in libraries), but also heat energy. Except in cold climates, this solar heat gain from daylight can be a burden on the building cooling system, and sunlight must be carefully controlled to avoid this.

But with good design, the daylight is not only a good source of light but the most efficient. The number of lumens per watt (efficacy) of daylight is twice that of a fluorescent lamp and ten times that of an incandescent lamp. Properly designed daylighting strategies can both reduce electric energy demand for lighting and minimize loads on the cooling equipment.   >>>

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Triangular skylights over the main reading room in the German National Library, Frankfurt Am Main. Image: Michael Bulander Relative efficacy of light sources (ratio of lumens of light energy per watt of power, or rate of heat energy supplied). Image: Edward Dean, AIA   Click on thumbnail images to view full-size pictures.