干旱区生态环境知识资源中心

The hot-arid climate of Phoenix, Arizona and much of the Southwest region of the United States typically experiences 325 days a year with clear sky conditions. This provides a tremendous opportunity for illuminating buildings with daylighting and thus a great opportunity for reducing the use of electric lighting dramatically

To determine the energy savings and the costs associated with a ''daylight-harvesting'' system, an automatic continuous-dimming system consisting of dimmable electronic ballasts and photosensor was installed.

The findings indicated that throughout the duration of the study, the dimming system reduced lighting energy consumption by approximately 75% during school hours.

Thirty classrooms with (16) four-lamp troffers can each be equipped with dimming systems for about $15,000 more than the cost of equipping it with standard electronic ballasts. The system can save $4,900 a year and has a payback of three years. Over the life-cycle of the equipment (estimated at 15-20 years), the dimming system can save a school more than $85,000.