If you want to really see the stars in the sky, how far would you have to travel from your front door?

Up until about 100 years ago, the night sky was dark, but with the ever-increasing use of artificial light, our world is illuminated almost 24/7. The result is light pollution, defined by the International Dark-Sky Association (IDA) as inappropriate or excessive use of artificial light. A nonprofit with more than 60 chapters around the world, the IDA advocates for "the protection of the night sky" and is recognized as an authority on light pollution.

There are several risks to this constant illumination:

Energy use

The federally funded National Optical Astronomy Observatory (NOAO) estimates that "poorly aimed and unshielded" outdoor lights waste more than 17 billion kilowatt-hours of energy each year in the U.S. Using citizen scientists, NOAO tracks light pollution with its Globe at Night program. More than 100,000 measurements have been contributed from people in 115 countries over the last nine years. The data shows that light pollution is a growing problem.

The U.S. Department of Energy estimates that 13 percent of home electricity usage goes toward outdoor lighting. More than one-third of that light is lost to skyglow — the artificial brightness of the night sky — resulting in about $3 billion wasted per year. About 15 million tons of carbon dioxide are released each year to power outdoor lighting, and the IDA estimates that wasted light releases 21 million tons of C02 annually.

From energy costs to C02 emissions, light pollution has an impact. International Dark-Sky Association

Disrupting wildlife and ecosystems

Light at night throws off the biological clocks of nocturnal animals. It can affect sea turtles in several ways, first by discouraging them from nesting, says the Sea Turtle Conservancy. Baby sea turtles, which hatch at night, typically find their way to the sea by looking for horizon lights. Artificial lights along the shore throw them off and draw them away from the ocean. Artificial lights can interfere with the migration patterns of nocturnal birds that use the stars and moon for navigation. Birds can become disoriented by lights and may collide with brightly lit towers and buildings. For frogs and toads, when nighttime croaking is interrupted, so is their mating ritual and reproduction.

"Wildlife species have evolved on this planet with biological rhythms — changing that has profound effects," Travis Longcore, a biogeographer with the Urban Wildlands Group in Los Angeles, told National Geographic.

A rare display of the aurora borealis shows a red glow over Borrego Springs, California. Dennis Mammana/International Dark-Sky Association

Health concerns

Some studies have linked artificial light at night to increased risk of diabetes, obesity, depression and some cancers, as well as obvious sleep disorders. Specifically, when our bodies don't spend enough time in the dark, we don't make enough of the hormone melatonin. Melatonin helps maintain your sleep-wake cycle, as well as regulate some of your body's other hormones. It may have other key roles, including strengthening the immune system.

The American Medical Association even released a report called "Light Pollution: Adverse Health Effects of Nighttime Lighting." The report is a review of research that looks at nighttime lighting and its health affects on people. The study concludes: "The natural 24-hour cycle of light and dark helps maintain precise alignment of circadian biological rhythms, the general activation of the central nervous system and various biological and cellular processes, and entrainment of melatonin release from the pineal gland. Pervasive use of nighttime lighting disrupts these endogenous processes and creates potentially harmful health effects and/or hazardous situations with varying degrees of harm."

The Church of the Good Shepherd at Aoraki Mackenzie International Dark Sky Reserve in New Zealand. Fraser Gunn/International Dark-Sky Association

Dark Sky Places

Because light at night can be so potentially problematic, the IDA created the Dark Sky Places Program in 2001 to encourage communities worldwide to adapt responsible lighting policies to cut back on light pollution. There are currently 60 communities, parks, reserves, sanctuaries and planned developments that have met the program's rigorous standards and fulfilled the application status to achieve official Dark Sky Places designated status.

For example:

A camper sleeps under the night sky in Dripping Springs, Texas. Rob Greebon/International Dark-Sky Association

In Dripping Springs, Texas, all holiday lights must be small bulbs on a strand, low-output lamps to light up yard art, or temporary spotlights with illumination that can't be seen from anyone else's property.

The Milky Way sets over the Cosmic Campground, New Mexico, with the lights of Morenci, Arizona, in the distance. David Thornburg/International Dark-Sky Association

There's no permanent, artificial lighting at the Cosmic Campground in western New Mexico. One of only two Dark Sky Sanctuaries, it gives campers a 360-degree unobstructed view of the night sky. The nearest significant source of electric light is more than 40 miles away, across the border in Arizona.

New lighting fixtures help protect wildlife in Indiana Dunes National Lakeshore around Beverly, Indiana. Pat (Cletch

In Beverly Shores, Indiana, the town's original 61 streetlights were retired or replaced with high-pressure sodium fixtures, which helped to protect several species in the Indiana Dunes National Lakeshore, the park that surrounds the town.

The night sky over Coll, Scotland. Olvin Smith/International Dark-Sky Association

There are no streetlights on the Isle of Coll in Scotland, and all businesses and homes are encouraged to turn off or reduce outdoor lighting at 10 p.m.

The lighting management at Hortobágy National Park in Hungary focuses on avian protection. International Dark-Sky Association

In Hortobágy, Hungary’s first national park, lighting has been retrofitted to protect the many birds that have a home in the park's marshlands. There are also nighttime walks that include education about light pollution, and the park has plans to build an observatory.

Making lighting changes

If you don't live in an official Dark Sky Place, that doesn't mean you can't take steps to help dim the lights. The IDA suggests:

Don’t light an area if it’s not necessary.

Turn off lights when you're not using them.

Don’t use excessive illumination.

Use timers, dimmers and motions sensors when possible.

Use only "full cut-off" or "fully shielded" lighting fixtures.

Use energy-efficient lighting sources and fixtures.