Look up on a clear night in Austin, and you may see a handful of stars. Do the same thing out in the backcountry at Big Bend, and the stars are far too numerous to count.

The sky over both locations is the same, of course. What’s different is the amount of outdoor lighting competing with those little twinklers. The International Dark Sky Association estimates that outdoor lighting that shines directly upward wastes more than $2.2 billion worth of electricity in the US each year, the equivalent of 12.9 million barrels of oil or 451.8 million gallons of gas.

Excessive and mis-directed light also makes night time so bright that some 40 percent of Americans never even adjust to night vision. Two-thirds of our population can no longer see the Milky Way in the skies over their home.

This isn’t bad news just for penny pinchers and stargazers, either. Scientists are finding that artificially bright nights have an effect on our natural world, from navigation and reproduction in animals to dormancy and growth in plants — and even our own health.

For example, too much light at night can affect our circadian rhythm, a 24-hour internal clock that controls hormone production, cell growth, and psychological changes in our bodies. This disruption has been shown to significantly increase the risk of breast cancer and possibly other diseases. Bright nights may even cause depression and contribute to obesity.

Artificial light disrupts the annual migrations of bird, putting some 450 migrating species at risk. Research has shown that certain wavelengths of artificial light can disrupt a bird’s sensitivity to the earth’s magnetic field, affecting their navigation ability. Birds are drawn to lighted structures at night, says John Arvin of the Gulf Coast Bird Observatory, gcbo.org where they circle, often striking guy wires, the lighted object, or each other — or drop to the ground exhausted. Lighted structures cause as many as 100 million bird deaths in North America every year.

Hatching sea turtles instinctively turn away from the darkness of sand dunes behind the beach toward the open, lighter sky over the ocean. Artificial light disorients hatchlings, putting them at risk of dehydration, exhaustion, predation and being run over.

Nocturnal frogs suspend normal feeding when exposed to light, and male tree frogs may stop calling in areas with bright lights, which affects their ability to successfully mate and reproduce.

Insects suffer from increased predation around lights, and from a trapping effect that kills billions of them each year. You may not care about a bunch of dead bugs, but they’re a critical part of a healthy ecosystem, serving as food for animals and pollinators for plants.

Anyone who has ever grown plants under artificial light indoors knows that plants are affected it — but not always in a good way. Photoreceptors in plants detect changes in day length, with longer winter nights triggering fall leaf loss. Urban trees may shed their leaves late, which makes them vulnerable to damage from cold and could restrict leaf growth the following spring.

In fact, many plant processes are light sensitive and potentially affected by artificial light. Bright lights have been shown to delay seasonal dormancy or dieback, and even flowering and fruit production. Plants are also affected when light affects pollinators such as birds and bats, and herbivores, which spread the seeds of many plant species.

While much light at night is simply the result of poor design or carelessness, ironically, some is actually intended to make us safer. But according to the IDA, studies have indicated that there is no conclusive correlation between night lighting and crime. In fact, bad lighting can create shadows where the bad guys can hide and glare that actually makes it harder to see. Permanent lights actually allow criminals and vandals to see what they’re doing, the IDA reports. Schools that adopted timed and motion-activated lights, rather than always-on light, saw decreased vandalism and graffiti.

Fortunately, this is an easy-to-solve problem. Eliminate or turn off unnecessary lights. Shield lights and focus lighting toward the ground or onto signage. Eliminate all upward-directed decorative lighting. You'll save energy and money. And we'll all enjoy the stars.