A new study aims to provide some guidelines for the use of LED lights, which are quickly taking over the global lighting market but are known to create serious problems for wildlife and people.

“LEDs are a major focus of this paper because they are replacing existing outdoor lighting at a rapid pace and that is changing the nature of the outdoor environment in a way that is not going to be stopped,” says Travis Longcore of the University of Southern California.

By 2020, LED lights are projected to account for 69 percent of the global market, a dramatic increase from nine percent just seven years ago. “LEDs are coming, but we can perhaps guide some of the ways in which they're used and the choices that are made relative to wildlife, because the color of light matters to wildlife," Longcore says. "It also matters to people and the circadian rhythms of life on Earth.”

A USC press release on Longcore's study says: "A central component of the USC research includes the first publicly available database showing how about two dozen different types of artificial lighting affect wildlife. The matrix is called 'Rapid Assessment of Lamp Spectrum to Quantify Ecological Effects of Light at Night.' Developers, land-use planners and policymakers can use it to choose lighting that balances the needs of nature and people. Today, regulations to limit light direction or intensity typically don’t account for the different hues of LED lights."

In effect, Longcore says, the explosion of artificial light all across the world is a “massive public health experiment." Excluding organisms that live in caves, where there is never a daily, annual or lunar rhythm, every organism is cued into patterns of light and dark, he explains. LED lights come in many colors and each organism responds in a unique way to the different wavelengths.

Blue, white and other short-wavelength colors tend to be more disruptive to animals, while yellow, amber and green are less harmful. Sometimes these lights can be fatal: Female sea turtles, for example, like to lay their eggs only on beaches that are dark, so they will avoid bright beaches, which could mean they would not find a suitable spot to lay their eggs.

Sea turtle hatchlings incubate under the sand, hatch at night and must get to the ocean as fast as possible. Since the hatchlings are born with the instinct to move away from the darkest horizon, artificial lighting such as porch lights or street lights will cause the hatchlings to go away from the ocean instead of toward it. This can result in the hatchlings being run over by cars or eaten by predators.

A similar thing happens to Newell's shearwater, a long-winged seabird. Fledglings emerging from the nest are attracted to lights on the coast and can end up stranded on the ground, unable to make their way to the ocean environment where they belong.

Juvenile salmon are also attracted to lights as they move upstream and downstream, which can put them in danger. “There's actually a neat study showing that seals will line up underneath bridge lights and pick off the salmon as they get attracted to the lights,” Longcore explains. “The light affects the timing and synchronization of their movements and makes them more likely to be exposed to predators.”

In humans, there are “epidemiological correlations” and experiments which show that increased light exposure is associated with an increase in certain diseases, like breast cancer and prostate cancer, Longcore says. Exposure to light also leads to sleep disruption, which can have a whole series of adverse consequences, including diabetes and depression.

For outdoor lighting, color temperature is just one of several ways to reduce health impacts, Longcore says. “It's also about directionality — having a shielded light that only goes down where you need the light, using the lowest intensity that you can, and duration — using a motion detector instead of a dusk-to-dawn light. And then, of course, always asking the question, ‘Do I need this light or is there another solution?’”

For example, instead of lighting a pathway on a campground or in a parking lot, the pathway could be created with white gravel, which reflects the ambient light and “illuminates” the path. This simple solution to a common problem doesn’t disrupt wildlife or diminish the outdoor experience.

This article is based on an interview that aired on PRI's Living on Earth with Steve Curwood.