Pauline Anderson

March 11, 2016

Too much night-time street lighting strongly affects sleep habits and daytime functioning, a new study suggests.

It has long been suggested that excess light interferes with sleep, but now, researchers actually have "proof," said lead author Maurice M. Ohayon, MD, PhD, professor, psychiatry and behavioral sciences, Stanford University, and director, Stanford Sleep Epidemiology Research Center, California.

Their findings were released March 1 and will be presented at the upcoming American Academy of Neurology (AAN) 2016 Annual Meeting.

For the study, researchers interviewed a representative sample of 15,863 people across the United States by phone from 2002 to 2009. They asked participants about their sleep habits, including when they went to bed and how much sleep they got, during the week and on weekends. Participants reported on these sleep habits during the past week, past month, and past year.

Participants also provided information on their eating habits, including time and composition of meals, their medical and psychiatric disorders, and their stress levels.

To determine the amount of external light participants were exposed to, researchers used night-time light radiance (NLR) data from Defense Meteorological Satellite Program's Operational Linescan System.

Precise Measures

These data provide the radiance "geolocation" by latitude and longitude, or the precise measure of external night-time radiance based on addresses, according to Dr Ohayon.

"We knew the precise address, the zip code, of each subject, so from the satellite, we obtained the amount of radiance that each subject had at the time of the interview."

The satellite measures all the radiance in a particular zone, so the only difference between NLR in urban areas and that in rural zones would be the amount of street lighting, said Dr Ohayon.

After controlling for all variables, including stress, which can affect sleep, the study found that outdoor NLR was associated with delayed bedtime and wake-up times (both P < .0001). NLR was also associated with a shortening of sleep duration (P < .01).

"People with high light exposure slept an average of 402 minutes per night, compared to 412 minutes for people with low light exposure," said Dr Ohayon.

Exposure to greater NLR was also associated with increased daytime sleepiness (P < .0001), and the likelihood of having a circadian rhythm disorder and of being dissatisfied with sleep quantity and quality (both P < .0001).

Of the participants living in area with high radiance, 16% were dissatisfied with their sleep quality or quantity compared with 7.2% in areas with low radiance, noted Dr Ohayon.

The study found other differences between those with high compared with low NLR, including the following:

  • "Confusional arousals": 18.8% vs 13.3%;

  • Fatigue levels: 9.4% vs 7.2%; and

  • Excessive sleepiness plus impaired functioning: 6.1% vs 1.9%.

"So you can say that practically 4% (the difference in excessive sleepiness and impaired functioning between high and low exposures) is due to the light in the environment," said Dr Ohayon.

He noted that daytime sleepiness can contribute to traffic accidents; reduced efficiency and cognitive functioning at work; and mood issues, such as depression, irritability, and anger.

Biggest Sample

A strength of the study is its sheer size, said Dr Ohayon. "I think it's the biggest sample of the general population that exists presently in this field."

Another "big advantage" of the study is its longitudinal design, spanning more than 12 years, he said.

And a "very original" element to the study is that it included geolocation of radiance, stressed Dr Ohayon. "We knew precisely, point by point, the amount of radiance that each geographic zone was receiving."

Street lighting has had positive effects on the urban environment, such as improved security and safety because of fewer accidents, but it comes at a price, said Dr Ohayon. That cost, he said, is that the day is being extended and "there is no more night."

The consequences of this, he added, are that our internal biological clock or circadian rhythm gets out of sync. That clock is dependent on the secretion of melatonin, which normally occurs with natural darkness as night falls.

This encroaching of daytime into the evening is a public health issue, according to Dr Ohayon. He suggests designing light-emitting diode lighting according to the nature of the neighborhood: blue in areas with high traffic (blue mimics daylight so drivers would be more apt to stay awake and cause fewer accidents) but more calming yellow or orange tones in residential areas.

At the individual level, things like blackout curtains in the bedroom might improve sleep, as could eliminating light sources near the bed. The worst scenario for sleep is to "fall asleep on the sofa in the living room with all lights and monitors on," said Dr Ohayon. "That is guaranteed to destroy your next day."

Commenting on these new findings is Nathaniel F. Watson, MD, professor of neurology at the University of Washington in Seattle, co-director of the University of Washington Medicine Sleep Center, director of the Harborview Medical Center Sleep Clinic, and president of the American Academy of Sleep Medicine.

"The natural, daily rhythm of sunlight and darkness is one of the most influential timing cues that helps your body regulate your sleep schedule," Dr Watson told Medscape Medical News.

"The widespread presence of artificial light from indoor and outdoor lighting, as well as brightly lit smartphone and tablet screens, can have a disruptive effect on your sleep timing and sleep quality," he added. "This study is a reminder that we should limit our exposure to bright light at night and create a dark bedroom environment that promotes healthy sleep."

The study was supported by the John Arrillaga Foundation, the Peter Bing Foundation, and the Philip Stein Foundation.

American Academy of Neurology (AAN) 2016 Annual Meeting. Abstract 2778.

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