Bright city lights: more security, less sleep.
In 1879, the first street lighting illuminated New York; now, there is hardly a place in the world that escapes the glow of the electric light.
Lights blaze on streets and highways, in yards, parking lots and on billboards and sports facilities, illuminating cities in particular for miles around.
One study reports that in 2009, the sky glow of Los Angeles could be seen from an airplane 200 miles away, and that in 1994, when an earthquake temporarily switched off the power supply, a strange "giant, silvery cloud" in the dark sky caused public concern. It was the Milky Way.
The Centers for Disease Control and Prevention (CDC) link a number of conditions to lack of sleep, including diabetes, cardiovascular disease, obesity and depression, as well as injury and disability resulting motor-vehicle and machinery-related trauma caused by sleepiness. They estimate that 25% of Americans sometimes lack sleep and that chronic insomnia affects 10% of the population.
Dr. Maurice Ohayon, PhD, of Stanford University in Stanford, CA, and colleagues interviewed 15,863 participants by phone over an 8-year period, to find out about people's sleep habits and sleep quality, as well as medical and psychiatric issues.
29% of people in well-lit areas dissatisfied with sleep
The team then used nighttime data from the Defense Meteorological Satellite Program to establish how much outdoor light the same people were exposed to at night.
Results showed that in urban areas with more than 500,000 people, exposure to light is three to six times more intense than it is in small towns and rural areas, and that nighttime light disrupts sleep duration and leads to sleep disturbances.
Residents of more intensely lit areas had a 6% higher chance of sleeping less than 6 hours per night, and 29% of them were dissatisfied with their sleep quantity or quality, compared with 16% in less well-lit areas. Those exposed to bright lights slept an average of 412 minutes per night, compared with 402 minutes in darker areas.
In well-lit areas, people were 9% more likely to experience fatigue, compared with 7% of people in less well-lit locations.
High levels of light exposure were more likely to cause people to wake up feeling confused during the night, with 19% experiencing nighttime confusion, compared with 13% in less illuminated places.
Excessive sleepiness and impaired functioning affected 6% of people in highly lit areas, compared with 2% elsewhere.
Study author Dr. Maurice Ohayon comments that all large cities create light pollution, and that this exposure may cause excessive sleepiness and affect how people function during the day.
Dr. Ohayon says:
"Our world has become a 24/7 society. We use outdoor lighting, such as street lights, to be more active at night and to increase our safety and security. The concern is that we have reduced our exposure to darkness, and it could be affecting our sleep."
If other studies confirm the results, he suggests that room-darkening shades or sleep masks could help to combat the problem.
Medical News Today recently reported that a lack of sleep can increase the desire to eat, and in particular, to indulge in unhealthy snacks.