Natural Light Co. The company's active system adds a rotating mirror assembly to catch the very low-angle light that the sun produces at dawn and dusk. The assembly follows the sun using a pair of IR photodiodes and has been wind-tested to 90 miles per hour. The passive system is designed to eliminate the need for electric lights from two hours after sunrise until two hours before sunset. The active system can extend the period of useful daylight by two hours. The company's largest market so far has been classrooms in the southeast because of the high availability of sunlight in the area, according to Lancing.
Schools benefit because they operate during daylight hours, with little use after dark.
LightScience makes an active system enclosed in a fiberglass shell that protects it from the elements. Its tilting mirrors track the sun on horizontal and vertical axes. According to Lee Webster, company president, the biggest marketing hurdle is convincing building owners to make holes in their roofs. The performance of the active unit is equivalent to that of a passive skylight during the middle part of the day, but its biggest advantage comes during periods of low-angle sunlight, when it can collect light that a passive skylight can't. Webster admits that cloudy days still pose a problem because the housing and mirrors actually reduce the amount of light that comes in.