U.S. federal buildings save 75% energy with daylighting

Using daylight to reduce artificial lighting saves much more energy than has been previously thought. The U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy has reported that energy savings of up to 75 or 80 per cent have been seen in U.S. federal buildings with daylighting designs.
Proper daylighting design involves much more than adding windows or skylights. It requires balancing the natural light with heat gain and loss, glare control and variations in daylight availability.
Clerestories and orientation of windows and skylights play a part, and skylights can be unconventionally shaped such as in domes or hemispheres to guide the daylight through a reflective shaft. A diffuser at the bottom of the shaft minimizes glare and heat from the light beam.
Most energy managers are familiar with the fast payback on conventional building lighting upgrades, says a report in FEMP, the department’s publication, but many are surprised that daylighting projects pay back just as fast or faster. A hangar at Fort Huachuca, near Tucson, Arizona, was retrofitted with 36 daylighting units at a total cost of $45,000. Each unit installed displaced a 1,175-watt light fixture. Over a 35-month period the devices saved a total of 268,990 kWhours, amounting to savings of U.S. $9,600 a year and a payback of 4.7 years.