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Anatomy of active daylighting

About the only things in common that active daylighting has with traditional skylights is a weather-proof domed cover and light well. What's different about active daylighting is what makes it one of the most effective daylighting technologies available today.

Inside the domed cover is a single, highly reflective, angled mirror driven by a solar-powered electric motor. The units require no line voltage so wiring is unnecessary. A global positioning system (GPS) that "knows" its latitude and longitude and its orientation to the sun is the unit's "brain." An energy storage capacitor provides supplemental power to the GPS and motor on successively cloudy days. Because the units install over an entire roof, they can provide light deep inside a building.

Before the sun rises, the GPS signals the motor to rotate the mirror to the exact position where the sun will crest the horizon. The mirror "locks" onto the rising sun and begins reflecting light down into the light well. The mirror follows the sun as it arcs across the sky during the day. The GPS accounts for varying lengths of daytime throughout the year and the sun's position from season to season.

The intense, reflected daylight passes through a prismatic lens positioned between the mirror and the light well. The lens diffuses the light and helps minimize solar heat gain in the building's interior.

A decorative lens at the bottom of the light well further diffuses light, virtually pouring it into the building interior. The illumination is uniform, glare free and without the hot spots that sweep across a room from a skylight as the sun arcs across the sky. The lens also keeps conditioned air from escaping up the light well.

The cool thing about thermal design

So effective is the unit's thermal design that it produces less than half the heat generated by fluorescent lighting, reducing cooling costs by a 0.4W for every one watt of lighting saved. Since the light produced by each daylighting unit is equivalent to an 800 watt fluorescent lamp, cooling loads would drop by 320W of power per unit, or 21,120W (21.12 kW) for all 66 units school-wide.

Considering the same parameters used to calculate lighting savings, the total energy saved by lowering cooling demands could be 38,016 kWh of electricity. With the 7.8 cent kWh rate that the school pays, the savings in taxpayer dollars would be $2,965 a year. Adding this to the $7,413 in lighting savings produces a total of $10,378 in taxpayer dollars saved per school year.

Realistically, savings would be even higher since utility rates often rise during peak demand for electricity, generally in the late afternoon during hot weather, which is abundant in Las Vegas. Peak rates can be double or triple normal rates and would quickly escalate savings.

Saving taxpayer dollars isn't the only benefit of the daylighting units. The light they reflect inside the school is pure, natural illumination that's rated a perfect 100 on the color rendering index (CRI2.) and between 5000-6000 kelvin3. color temperature.

Fluorescent lamps in comparison can offer daylight-level color temperatures, but typically achieve CRI ratings in the mid eighties, quite a drop from the perfect 100 of daylight. It's a critical distinction as a series of lighting studies have shown.

The studies report that true daylight-quality lighting can produce important benefits for Desert Oasis students, teachers and staff. It's a bandwagon that everyone seems to be riding.

"Enhancing student performance was part of the motivation for integrating daylighting in the prototype schools," Kusz said. "There are a plethora of studies that report on the benefits of daylighting in schools and other types of buildings. Daylighting is more pleasant, less intrusive and less invasive than fluorescent lighting."

In fact, Kimsey sees a definite trend toward the application of daylighting in a range of buildings, but especially in educational facilities.

"Studies show that student test scores and attentiveness improve as a result of daylighting. We used those studies as a basis for incorporating daylighting into these prototype schools."

Young Leonard, vice president of SunStone Building Specialties in Las Vegas and the area's dealer for the Ciralight SunTracker, said, "Case studies have shown that daylighting can do everything—enhance grades, improve math scores, promote growth and deter tooth decay."

There's a third reason for daylighting's popularity. Leonard said, "Daylighting is now a focal point for architects. It's green. It was once considered a luxury. If the building was over budget, skylights were the first thing to be value-engineered out, but not any more."

1. IESNA: Illuminating Engineering Society of North America
2. CRI: Color rendering index is a measure of the quality of electric lighting in terms of rendering color accurately, compared to natural light, which is rated a perfect 100.
3. Kelvin (K): A measure of the appearance of light, from warm to cool. Warm light appears red, orange or yellow. Cool light appears white or blue. Sunlight has a color temperature of between 5000K-6000K, depending on time of day and cloud cover.