Advancing the effective use of light for society and the environment.

Thursday, April 14, 2005

Simple Daylight Harvesting Concepts Offer New Options for Energy Savings
Photo: Example of office daylighting

Lighting Research Center researchers have identified and evaluated new, simple concepts for daylight harvesting, a way to increase energy savings by taking advantage of the natural light entering a space through windows or skylights. The results of the study were recently published in Lighting Research & Technology. 

The research team, led by LRC Associate Director Russ Leslie, used computer simulations to compare a daylight-sensing switch and automatic blinds against existing daylighting systems to determine the most cost-effective method for reducing energy use. The simulations reflected both open and private commercial offices.

“Automatic switching is a daylight harvesting method designed for rooms with copious amounts of daylight,” said Leslie. “By taking advantage of natural light and using systems that turn off light fixtures for a portion of the day, we could significantly reduce energy consumption and the growing strain on the nation’s power grid.”

The U.S. Department of Energy estimates that lighting accounts for one-quarter of the total energy consumed by U.S. commercial businesses.

Improving upon existing technology

Typical daylight harvesting systems include a photosensor paired with a dimming ballast to control fluorescent lighting, dimming the lights proportionally to the amount of daylight entering the work space. However, full-dimming ballasts are expensive and photosensors are usually difficult to program and install.

The LRC set out to improve upon existing daylight harvesting technology and design a system that meets all of the following goals:

The research team proposed a combined system made up of a daylight-sensing switch, a self-adjusting device that simply switches lights on or off in response to the amount of daylight illuminance, and automatic blinds, a device that opens window blinds once per day. Occupants can close the blinds whenever they wish.

Realistic assumptions of people’s behaviors, such as the conditions prompting people to operate blinds or manual switches, were combined with daylight and illuminance data to develop an algorithm. The algorithm was used to calculate the energy use of the new, simple concepts, as well as existing dimming systems, and manual switching and blinds operation. Because climatic zones affect daylight availability, the calculations were done for all systems for six different climatic regions in the United States.

As the research team anticipated, the results showed that simplified daylight harvesting systems, such as the proposed daylight-sensing switch and automatic blinds, have the potential to provide energy savings. For example, for Albany, N.Y., the daylight-sensing switch and automatic blinds system showed an average annual energy savings of 24 percent compared with manual switching and blinds operation. In addition, the proposed technologies combined showed better performance during summer months compared to a photosensor-operated dimming system with manual blinds. The proposed simple technologies also are expected to be less expensive to purchase compared to dimming systems with automatic blinds.    

Additional results and details of the evaluation can be found in the journal article “The potential of simplified concepts for daylight harvesting”  by Leslie, Raghavan, Howlett, and Eaton, published in Lighting Research & Technology volume 37, issue 1.

Lighting Research & Technology is an internationally renowned journal disseminating the latest research in all areas of illuminating engineering. 

Daylight Dividends

The development of the daylight-sensing switch and the evaluation of the simplified daylight harvesting concepts were supported by the Daylight Dividends program, a national effort administered by the Lighting Research Center to educate and provide evidence, guidance, and perspectives supporting the use of daylighting in commercial and educational facilities. Program sponsors include California Energy Commission, Connecticut Light and Power Company, Iowa Energy Center, New York State Energy Research and Development Authority, North Carolina Daylighting Consortium, Northwest Energy Efficiency Alliance, and the U.S. Department of Energy.

About the LRC

The Lighting Research Center (LRC) is part of Rensselaer Polytechnic Institute and is the leading university-based research center devoted to lighting. Founded in 1988, the Lighting Research Center has built an international reputation as a trusted and reliable source for objective information about lighting technologies, applications, and products. Its mission is to advance the effective use of light and create a positive legacy of change for society and the environment.



2005 Rensselaer Polytechnic Institute, Troy, NY 12180 USA.

Rennselear Polytechnic Institute