Biological rhythms come under the spotlight

04 Jan 2007

US researchers are exploiting a specially designed optical sensor to investigate the effect of light on our biological clock.

Scientists at the Lighting Research Center (LRC) of the Rensselaer Polytechnic Institute in the US are forming a worldwide user group of scientists, lighting equipment manufacturers and physicians to better understand how light affects human biological rhythms. Knowledge gleaned from the research could lead to new therapies aimed at controlling the body's sleep/wake cycle and hormone production mechanisms.

"Circadian (or biological) rhythms are physiological processes that recur every 24 hours and are synchronized by a biological clock in the brain," the LRC's Andrew Bierman told optics.org. Light falling on photoreceptors in the retina causes a signal to be sent to the brain, which then regulates the biological clock.

Under natural lighting conditions, this process synchronizes the body to the solar day. The goal of Bierman's team is to find out precisely how much incident light is needed to bring about changes in the body's internal clock.

Daysimeter

To achieve this goal, Bireman's team has designed and built the Daysimeter, which from the outside resembles a microphone headset. Instead of a microphone, two small cylindrical tubes projecting outwards from behind the ear incorporate sensors to record the quantity of blue and photopic light (Meas. Sci. Tech. 16 2292).

"At this point, we do not know what level of precision is needed for characterizing a person's light exposure to bring about measurable changes to the circadian system," said Bierman. "The Daysimeter is an instrument for measuring circadian stimulus while at the same time helping to define and redefine what constitutes circadian light."

The device can continually measure the duration and the quantity of optical radiation incident on the eye for at least a week. Information on the head angle and user activity can also be captured, which will help researchers to develop a better understanding of how light affects the circadian system. For example, researchers at the Harvard School of Public Health are currently using the Daysimeter to study how hospital lighting affects hormone production in nurses working the night shift.

Engineers can also use this data to design lighting products for people suffering from illnesses that cause them to be confined indoors all day. "One idea is to have the spectrum and quantity of the lighting vary throughout the 24 hours to provide the necessary contrast to the circadian system," says Bierman. Specialized lighting could also help travellers to overcome jet lag more quickly.