How light and dark night skies affect your health


I hope you had time for a summer road trip with wide open spaces, vast starry skies and new experiences. And as you headed toward home late at night you may have been beckoned by the orangey glow of your town or city awaiting your return. As you pulled into the garage, you may have taken one last look outside before you started to unload the car and return to life as usual. In your tired and wistful state, you may or may not have noticed ... where did all the stars go?

We may be able to see a few of the main constellations, but the gauzy brushstrokes of our galaxy and beyond are gone, victims of light pollution.

NASA and other partners recently produced a Global Night Sky Atlas that shows us one in three humans on Earth cannot see the Milky Way when they look up at the night sky. Four out of five Americans cannot see a natural night sky because of light pollution.

While we appreciate the ability to work, play, travel and read at night, there are some surprising negative consequences.

Research links the brightening night sky directly to negative impacts on human health and immune function, and on unfortunate behavioral changes in insect and animal populations. Poorly designed and implemented lighting actually decreases safety and wastes an exorbitant amount of energy.

New LED systems may be more economical, but produce harsher bright light with lots of blue wavelength which increases scatter into the environment. Blue light has a direct impact on melatonin secretion in humans and disrupts normal circadian rhythm.

Light pollution is excessive, inappropriate and obtrusive artificial light. The four components of light pollution are often combined and may overlap:

• Urban Sky Glow — the brightening of the night sky over inhabited areas. (Goodbye, Milky Way.)

• Light Trespass — light falling where it is not intended, wanted, or needed. (Your neighbor's porch light is always on and shines into your bedroom.)

• Glare — excessive brightness which causes visual discomfort. High levels of glare can decrease visibility. (Encountering high beams from oncoming traffic while driving.)

• Clutter — bright, confusing and excessive groupings of light sources, commonly found in over-lit urban areas. The proliferation of clutter contributes to urban sky glow, trespass and glare. (Think Times Square.)

One of my colleagues at Catalyst, Stefanie, lives south of Moorhead in the country with her husband and two small children who still occasionally awaken at night. They have a large shop on their property, and the yard is lit with several bright street lamps. The light penetrates into the bedrooms. One night after a surprisingly restful sleep for the whole family, she noted that the lamp closest to the house had burned out, making the bedrooms darker, allowing for better sleep. She was bummed when her husband replaced to bulb.

The World Health Organization and American Medical Association have both issued policy statements over the past decade warning that extended exposure to light at night increases the risk of certain cancers, probably via alterations to circadian rhythms, immune function and associated hormone levels.

Unfortunately, these studies did not distinguish between exposure to outdoor sources, like streetlights, and indoor ones, like television and smartphone screens. So the real risk may be underestimated.

A couple examples from the animal kingdom include migratory birds that drift off course and sea turtle hatchlings that never make it to the sea because of light distraction. More than half the Earth's species are nocturnal, so the effects are likely to be incredibly far-reaching.

Lead author of the Global Night Sky Atlas, Italian Fabio Falchi brings up a more intangible risk. "A starry sky is something that touches your soul," Falchi says. "Our civilization's religion, philosophy, science, art and literature all have roots with our views of the heavens, and we are now losing this with consequences we cannot fully know. What happens when we cannot be inspired by the night sky?"

So what should we do? Unlike some of today's complex environmental problems, many existing solutions to light pollution are simple, cost-effective and instantaneous.

• In the evening, avoid TV and screen time for at least one hour before bed. Consider the "night-time mode" on your phone and amber colored blue-blocker shades if you need to work on a late-night project.

• Make your bedroom very dark. Eliminate all the little blinking lights and use blackout shades. Eyeshades are good, but our skin also has photoreceptors, so emphasize total darkness as much as possible. Come up with a low-light way to make it to the bathroom without a fall or stubbed toe. Teach kids to sleep without a night light.

• Use motion sensors for security lighting around your home and property. Gather neighbors for a discussion so that others might be aware of how their lighting might affect others.

• Use warmer-colored LEDs that diminish the damaging blue spectrum.

• Talk to city officials about light pollution. Look to cities like Tucson, which has a dark sky policy.

Dr. Susan Mathison founded Catalyst Medical Center in Fargo and created Email her at