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

Thursday, July 15, 2004

Product development: ‘Daysimeter’ measures light for the circadian system
Photo: The Daysimeter
The Daysimeter

The effect of light on the circadian system is of growing interest in the health field. To help further research in this area, the LRC has developed a new tool designed to measure the level and spectral quality of light reaching a person’s circadian system.

The “Daysimeter” is a lightweight headset consisting of a photopic light sensor and a blue light sensor. The photopic light sensor can take illuminance measurements at the eye with an accuracy on par with standard, laboratory-grade photometry equipment. The blue light sensor’s sensitivity has a peak wavelength and spectral bandwidth that are a very close match with a proposed spectral sensitivity curve for the human circadian system.

“The close spectral match between the response of the photocell used in the Daysimeter’s blue light sensor and the proposed spectral sensitivity curve greatly reduces the need to filter the response, allowing us to use a smaller and less expensive detector assembly,” says Andy Bierman, LRC senior research scientist who led the development of the Daysimeter prototype.

Photo: LRC researcher Dr. John Bullough models the Daysimeter.
The Daysimeter's wearable design allows researchers to continuously measure light exposure.

Ongoing studies at the LRC are revealing that the spectral response of the human circadian system may result from a combination of photoreceptors that act in an opponent, or subtractive, manner (see April newsletter article, “LRC studies human response to light”). By employing two light sensors, the Daysimeter lends itself well to measuring the circadian response from light sources according to this opponent process. The impact of the opponent process on circadian light sensitivity can be evaluated by subtracting a portion of the photopic signal from the blue signal.

Field researchers currently measure light reaching the circadian system with conventional handheld light meters. However, it is often difficult to position these instruments near the eye to measure light exposure over a period of time. “With the Daysimeter, the process of measuring the quantity and spectral quality of light will become more accurate, allowing us to better estimate the impact of light on health,” says LRC Director Mark Rea, Ph.D.

Rea notes that the LRC plans to use the device to characterize the luminous environments of teens with delayed sleep phase syndrome, seniors with Alzheimer’s disease, premature infants in neonatal intensive care units, persons with seasonal affective disorder, and nurses working day and night shifts. The Daysimeter also will be used in daylighting research efforts.

Development of the Daysimeter was funded by the LRC's Daylight Dividends program. A technical product description is available on the Daylight Dividends Web site.

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.

© 2004 Rensselaer Polytechnic Institute, Troy, NY 12180 USA.

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