Daylighting is an aspect of green building design that should be ubiquitous; without adequate daylighting, people will not perform well and will not be healthy. For building plans, this implies a design that is no more than 66 feet wide, front to back, or about 33 feet to a window from any workstation. This is a standard design requirement in many places in Europe, where people's health is placed before economic efficiency. Looked at another way, a building should be oriented so that the long axis is east-west; this allows for maximum daylighting, from both south- and north-facing windows.

Daylighting's benefits are immediately apparent; people see better and feel better whenever there is natural light for reading and working. Good daylighting design can employ skylights, north-facing windows on the roof, a central atrium, light shelves to bounce light into a space while shading windows from the summer sun, and other techniques. Good daylight-

Daylighting at University of Oregon, Lillis Business School, Eugene, Oregon, designed by SRG Architects.

ing is always indirect, without glare. Daylighting is usually combined with electric lighting, so that there is a constant lighting level, typically 30 foot-candles at the desktop, or there is task lighting provided for each workstation.

According to a report from Carnegie Mellon University analyzing daylighting research, "Eleven case studies have shown that innovative day-lighting systems can pay for themselves in less than one year due to energy and productivity benefits...the ROI [return on investment] for daylighting is over 185%."38

A California study of the impact of daylighting examined 73 stores of a chain retailer, of which 24 had daylighting. The results:

The value of the energy savings from daylighting is far overshadowed by the value of the predicted increase in sales due to day-lighting. The profit from increased sales associated with daylight is worth at least 19 times the energy savings."39

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