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

Thursday, October 20, 2005

New Paper Details LRC Tool to Measure Light Exposure for Circadian System
By Jennifer Taylor
The Daysimeter
The Daysimeter measures light exposure at the eye.

The Lighting Research Center recently published details of one of its newest inventions, the Daysimeter, a field research tool designed to measure a person’s light exposure while going about a daily routine. Illuminance measurements recorded by the Daysimeter will help scientists studying the impact of light on health to understand how light affects the human circadian and visual systems.

The circadian system controls the body’s daily biological rhythms, such as the sleep/wake cycle and hormone production. Scientists have long known that light plays an important role in regulating circadian rhythms. In recent years, scientists and medical experts have explored how light exposure and circadian rhythms influence health. Studies have provided evidence of the effects of light on the development of premature infants, sleep for people with Alzheimer’s disease, and a potential link to the prevalence of breast cancer.

The lightweight, head-mounted Daysimeter measures both traditional (photopic) light levels and blue light levels that match an estimated spectral sensitivity of the circadian system. LRC Director Mark Rea, Ph.D., said, “The Daysimeter offers for the first time the possibility of moving from a general, imprecise definition of circadian light exposure to a much more precise and complete characterization. Accurate characterization of light as it impacts the circadian system may be one key to unlocking our understanding of a number of human health concerns.”

The paper, written by the LRC’s Andrew Bierman, Terence Klein, and Mark Rea, was published in the journal Measurement Science and Technology. It describes the Daysimeter’s components and mechanics, field trials, and research implications for the device. For more information about the Daysimeter, see the feature story published in the July 2004 LRC newsletter.

Dr. Rea said the instrument soon will be used in a number of field studies for circadian light measurement. Next year, the LRC will use the Daysimeter in clinical trials through Harvard University’s Nurses’ Health Study. The goal of that study is to investigate the impact of light exposure at night on breast cancer. “Our goal is to measure the entire 24-hour light exposure and quantitatively relate those light profiles to the probability of having breast cancer in night-shift nurses,” he said. In addition to the LRC focus on circadian light exposure, the center also plans to use the Daysimeter to better study the spectral response of the human visual system to glare from vehicle headlights at night.

A preprint of the paper, titled “The Daysimeter: a device for measuring optical radiation as a stimulus for the human circadian system,” is available on the Daylight Dividends Web site. The Daylight Dividends program sponsored the development of the Daysimeter.

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.

Rennselear Polytechnic Institute