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LIGHTING The creation of a new daylighting metric will help the buildings industry evaluate daylighting, and offers a better understanding of the quantity and quality of daylight in buildings
What qualifies a building as daylit? Could a room with just a single window be considered a daylit room? Or, should a room with floor-to-ceiling windows on all four sides be considered daylit? These are legitimate questions that are being asked by developers, owners, architects, and facility managers as the focus of green-building design shifts to daylighting.
There are two main reasons to bring daylight into a building: energy savings and human well-being. Lighting uses more energy in a typical commercial office building than any other single use (more than HVAC systems, computer equipment, etc.). Through the use of automatic controls (daylight harvesting), daylight offers the greatest potential to provide lighting energy and energy demand reduction during peak utility hours. Bringing daylight into a building so that it displaces electric lighting and provides sufficient illumination is one of the greenest ways to light a building today. When designed correctly, the lighting energy savings from turning off or dimming electric lights, and the resulting reduction in cooling loads, can offset additional heat gains or losses through the glazing to provide net-positive, whole-building energy savings.
While energy savings can be reason enough to promote daylighting in buildings, there is also growing evidence in the field of natural sciences that suggests a connection between daylight and human health. Studies have shown evidence of better student performance in daylit buildings, along with better productivity for office workers who have access to views and daylight during work hours. Exposure to daylighting during the day (and exposure to darkness during the night) has been shown to be directly linked to immune systems and health. As people spend more and more of their days indoors, the need for exposure to daylighting during the daytime is becoming even more important.
Measuring Daylight
So, how do you define a daylit building? To answer this question, there needs to be a metric to measure daylight, and a definition of criteria for acceptable daylight performance.
The most commonly used metric for measuring daylight in a building is called the "daylight factor" - expressed as a percent...