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Troy, N.Y. -  9/14/2011

LRC Study Challenges Claims that Satellite Images of Outdoor Lighting Predict Breast Cancer Incidence

Image of Earth's city lights by Craig Mayhew and Robert Simmon, NASA GSFC.A recent study conducted by the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute found that satellite images of outdoor lighting are unrelated to actual light levels reaching the eye. These results challenge previous studies linking satellite images of outdoor lighting with increased incidences of breast cancer. Light entering the eye regulates our body’s circadian rhythms, and disruptions in these rhythms may lead to serious health problems such as cancer. However, according to the LRC study, the spectrum, quantity, and duration of light exposure reaching the eye must be specified in order to determine the effects of light on human health, and satellite photometry cannot do this.

“After shift work was identified as a probable carcinogen by the World Health Organization, some studies were published that claimed a statistical association between light at night and the incidence of breast cancer. However, these studies relied on satellite photometry and subjects’ self-reports of bedroom brightness as measures of light exposure. None of these studies employed actual light measurements at the eye,” said LRC Director and principal investigator Mark Rea, Ph.D. “Before statistical associations between light at night and disease can graduate to a cause and effect relationship, it is necessary to measure the light as a potential causal agent. Our study showed no relationship between the measured light on the ground and the measured light in space.”

Scientists at the LRC are among many groups who have been working to identify factors, such as circadian disruption, that may lead to the higher incidence of breast cancer among rotating shift nurses. Patterns of light and dark are the main cues for synchronizing our internal biological clock with the 24-hour solar day, keeping us “in synch” and contributing to good health. These light/dark cues must, however, reach the retina, the back part of the eye, in order to have an impact on our circadian rhythms, according to Rea.

Project details
Using calibrated light meters, LRC scientists compared light levels in and outside the bedrooms of 72 female school teachers with satellite-measured light levels of ground brightness. The researchers then measured the 24-hour light/dark exposure of the teachers over the course of seven consecutive days. The subjects lived in a range of areas with both high and low amounts of sky brightness. These women were specifically selected because they did not work rotating shifts, which have been shown to place women at higher risk of breast cancer. If satellite measured levels of light were predictive of light exposures on the ground, irrespective of shift work, then those women who lived in bright areas might be at higher risk. The LRC study showed no relationship between satellite-measured light levels and actual light levels on the ground. 
A teacher wears a Daysimeter, an instrument developed by the LRC that measures light at the eye.In order to obtain accurate light exposure measurements at the eye, each teacher wore a Daysimeter, a small, head-worn device developed by the LRC to measure an individual’s exposure to the daily and nightly levels of “circadian light.” The definition of circadian light is based upon the potential for light to suppress melatonin synthesis at night, as opposed to measuring light in terms of how it stimulates the visual system. Melatonin is a hormone produced in the evening and under conditions of darkness, which acts as a timing messenger signaling to the body when it is nighttime. The researchers found that the teachers were all in synch with a regular 24-hour cycle, regardless of the sky brightness outside their homes.
“It is important to note, however, that these findings do not undermine the foundational data using animal models that link melatonin suppression by light at night and cancer risks, nor does it contradict the statistical association between shift work and breast cancer risk in humans. Rather, these findings simply undermine the inference for a causal relationship between light at night, as measured by satellite photometry, and breast cancer incidence,” explained Rea.
Rea carried out his study with LRC researchers Mariana Figueiro, Ph.D., and Jennifer Brons, who are also co-authors on a paper detailing the results. The study, “Measurements of light at night (LAN) for a sample of female school teachers,” is published in the journal, Chronobiology International, Volume 28, Issue 8. 
This project was funded by a grant from the Centers for Disease Control and Prevention; the Trans-NIH Genes, Environment and Health Initiative; and the National Electrical Manufacturers Association.

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 light and human health, transportation lighting and safety, solid-state lighting, energy efficiency, and plant health. 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. Learn more at

About Rensselaer Polytechnic Institute
Founded in 1824, Rensselaer Polytechnic Institute is America's first technological research university. Rensselaer encompasses five schools, 32 research centers, more than 145 academic programs, and a dynamic community made up of more than 7,900 students and more than 100,000 living alumni. Rensselaer faculty and alumni include more than 145 National Academy members, six members of the National Inventors Hall of Fame, six National Medal of Technology winners, five National Medal of Science winners, and a Nobel Prize winner in Physics. With nearly 200 years of experience advancing scientific and technological knowledge, Rensselaer remains focused on addressing global challenges with a spirit of ingenuity and collaboration.