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

Wednesday, January 12, 2005

How Does Light at Night Affect Your Health?
LRC presents findings on the effects of light at night

LRC researchers are updating the scientific, medical, and lighting communities regarding ongoing research in the area of light and health. The LRC’s continuing study of light’s impact on human and mouse circadian systems may help medical researchers to reassess important health issues such as potential cancer risks from light at night. This work includes exploring the implications of lighting from various light sources for different populations, including 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 who work day and night shifts.

Circadian responses to light, potential implications for cancer

Light at night can shift a body’s circadian rhythms, which regulate the sleep/wake cycle. However, light at night has other effects as well, including suppressing the production of the hormone melatonin. Because melatonin is an anticancer agent, light at night may actually contribute to increases in cancer cell growth. Therefore, understanding the characteristics of light that suppress melatonin production in humans is extremely important.

To disseminate the latest information on the biological effects of light, LRC researchers presented their findings on the biological effects of light and related subjects at several conferences during the fall of 2004.

In Vienna, Austria, Dr. Mariana Figueiro, head of the LRC’s Light and Health program, and LRC Director Dr. Mark Rea attended the Commission Internationale de l'Éclairage (CIE) conference, “Expert Symposium on Light and Health.” They provided new data supporting the phenomenon of spectral opponency in melatonin suppression. Their paper, co-written with LRC researchers Dr. John Bullough and Andrew Bierman, is called, “Spectral opponency in human circadian phototransduction: implications for lighting practice.”

Although melatonin is suppressed most by short-wavelength (blue) light, LRC studies suggest that when blue light is combined with longer wavelengths (to make white light), it becomes less effective as a stimulus to the circadian system. “Apparently the circadian system shares neural circuits with color mechanisms in the eye,” says Rea. (Read the study’s details in the April 2004 LRC newsletter.)

At the “Cancer and Rhythm” conference in Graz, Austria, LRC researchers advocated caution in interpreting research on rodent species with respect to light at night and cancer. At the conference, Rea and Figueiro presented a poster on this subject called, “Linking light at night to cancer risk in humans: does the evidence add up?” co-authored by Andrew Bierman and Terry Klein.

Most rodents are nocturnal and highly sensitive to light, according to Dr. Bullough, who studied lighting’s effect on mice. “A comparison of light levels needed to impact the circadian system shows that only very low levels of light are needed to impact a mouse’s circadian system,” says Bullough. “But very high levels are necessary to impact a human’s circadian system—more than 1,000 times the levels mice need.” LRC research also indicates that the circadian system of mice does not exhibit spectral opponency, so rodents should be relatively more sensitive to white light than humans.

Measuring light’s impact on the circadian system

As part of their study into the impact of light on the human circadian system, LRC researchers also have developed a unique light-measuring tool called the Daysimeter. The Daysimeter accurately characterizes spectral sensitivity to short-wavelength (blue) light; can incorporate spectral opponency; and can measure retinal light exposure rather than light on a desktop or other visual tasks. (Read more about the Daysimeter in the July 2004 LRC Newsletter.) The project was sponsored by the Daylight Dividends program.

Rea spoke about the Daysimeter at “Emerging Topics in Breast Cancer and the Environment Research,” a conference held in Princeton, N.J. Dr. Rea presented an informative poster co-authored with Bierman and Klein titled “Of mice and women: Light at night and cancer risk,” describing the light-measuring characteristics of the Daysimeter. He received funding for his travel from the Susan G. Komen Breast Cancer Foundation.

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