5. The sky glow of Los Angeles is visible from an airplane 200 miles away.

Residents of L.A. haven’t been able to see the stars for a while. In fact some city dwellers don’t even know what a natural night sky looks like. When a 1994 earthquake knocked out the city’s power, many anxious residents called local emergency centers to report a strange “giant, silvery cloud” in the dark sky. What they were seeing – for the first time – was the Milky Way, long obscured by light pollution. Photo credit: Bryce David (CC).

4. Artificial light at night disrupts the seasonal cycle of trees.

Even plants depend on the natural cycle of day and night. Artificial light at night can throw off a plant's response to the change of seasons. Prolonged exposure to artificial light prevents many trees from adjusting to seasonal variations. Notice how the leaves of this tree have their fall colors, except for those directly under the streetlight (upper right). This, in turn, has implications for the wildlife that depend on trees for their natural habitat. Photo by Fraser Clarke.

3. Light Pollution unnecessarily contributes to climate change.

In an average year in the U.S., outdoor lighting uses some 120 terawatt-hours of energy, mostly to illuminate streets and parking lots. That’s enough energy to meet New York City’s total electricity needs for 2 years. Unfortunately, up to 50 percent of that light is wasted. That adds up to $3.3 billion and the release of 21 million tons of CO 2 per year! To offset all that CO 2 , we’d have to plant 875 million trees annually. Photo by Jim Richardson.

2. Light pollution kills millions of birds a year.

Artificial lights can disrupt the migratory schedules of birds causing them to leave too early or too late in the season, missing ideal conditions for nesting. Birds that navigate by moonlight and starlight can wander off course. Millions die every year by colliding into needlessly illuminated buildings. Every year, the Fatal Light Awareness Program (FLAP) “displays” these victims of light pollution to raise public awareness (above). Photo by Kenneth Herdy, Fatal Light Awareness Program.

1. Exposure to artificial light at night puts your health at risk.

Humans evolved with the rhythms of the natural light-dark cycle of day and night. Due to artificial light, most of us no longer experience truly dark nights. Like most life on Earth, we adhere to a circadian rhythm — our biological clock. Natural light is an important cue that helps the set our clock to Earth’s 24-hour rotation period. Exposure to artificial light at night disrupts this process, increasing our risks for cancers and other potentially deadly diseases. Blue-rich light at night is particularly harmful. Unfortunately, most LEDs used for outdoor lighting, computer screens, TVs, and other electronic displays emit abundant blue light.

The good news is YOU can make a difference!

Make sure your lighting is shielded so lights shine down and not up

Use energy saving features like timers, dimmers and motion detectors

Talk to your neighbors about good lighting

Tell you friends and family to limit their exposure to blue light at night

Become a member of the International Dark-Sky Association.

Cheryl Ann is IDA’s Communications and Public Affairs Director. She’s an outdoor enthusiast regardless of whether it is day or night. Growing up in rural Washington state, she learned to appreciate night skies at an early age. Before joining IDA, she received graduate degrees in mass communication and then taught college communication courses. Prior to her graduate studies, she worked in public relations for state and municipal agencies. Cheryl Ann has published numerous freelance articles, chapters, and a book. She’s excited that she gets to use her writing and communication skills for such a great cause. In her free time Cheryl Ann loves to explore the beautiful Sonoran Desert (Ariz.), garden, play music and take pictures.