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Troy, N.Y. -  6/25/2010

Researchers define light as it impacts the human circadian system

Photo Credit: National Institute of General Medical SciencesIn a paper recently published in the Journal of Circadian Rhythms, researchers at Rensselaer Polytechnic Institute's Lighting Research Center (LRC) have defined light as it impacts the human circadian system.  Circadian rhythms are biological rhythms that repeat approximately every 24 hours. Exposure to the natural sunrise and sunset synchronizes our circadian rhythms to exactly 24 hours. Circadian disruption by irregular light/dark patterns have been associated with increased risk for breast cancer, diabetes, obesity, heart disease, sleep disorders, and other ailments. 

LRC researchers coined the term “Circadian Light” as spectrally weighted retinal irradiance that stimulates the human circadian system.  The definition of circadian light is based upon the potential for light to suppress melatonin synthesis at night.  Melatonin is a hormone produced at night and under conditions of darkness and is used as a marker of the circadian system. Formally, light is defined in terms of how it stimulates the human visual system, but this limited definition precludes the impact that light has on other biological systems, such as the circadian system.  Because exposures of light and dark on the retina regulate the circadian system, and because circadian disruption has broad health implications, it is important to develop a new definition of light that characterizes the impact light has on this important biological system.

“As the conversation about circadian light evolves,” said LRC Director Mark Rea, “it will become necessary to develop a formal spectral sensitivity function for the circadian system based on the neuro-anatomy and neuro-physiology of the retina.”

The paper, “Circadian Light,” utilizes a discussion of light for human vision to lay a foundation for a definition of Circadian Light (CL).  Reference is also made to the Daysimeter used as a practical field device to measure personal light exposures in everyday life.  An electronic version of this article can be found online at:

About the Lighting Research Center
The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute is the world's leading center for lighting research and education. Established in 1988 by the New York State Energy Research and Development Authority (NYSERDA), the LRC conducts research in solid-state lighting, light and health, transportation lighting and safety, energy efficiency, and plant pathology. LRC lighting scientists with multidisciplinary expertise in research, technology, design, and human factors, collaborate with a global network of leading manufacturers and government agencies, developing innovative lighting solutions for projects that range from the Boeing 787 Dreamliner to U.S. Navy submarines to hospital neonatal intensive-care units. In 1990, the LRC became the first university research center to offer graduate degrees in lighting and today, offers a M.S. in lighting and a Ph.D. to educate future leaders in lighting. With 35 full-time faculty and staff, 15 graduate students, and a 30,000 sq. ft. laboratory space, the LRC is the largest university-based lighting research and education organization in the world.

About Rensselaer Polytechnic Institute
Rensselaer Polytechnic Institute, founded in 1824, is America's first technological research university. The university offers bachelor's, master's, and doctoral degrees in engineering; the sciences; information technology and web sciences; architecture; management; and the arts, humanities, and social sciences. Rensselaer faculty advance research in a wide range of fields, with an emphasis on biotechnology, nanotechnology, computational science and engineering, data science, and the media arts and technology. The Institute has an established record of success in the transfer of technology from the laboratory to the marketplace, fulfilling its founding mission of applying science "to the common purposes of life."