Midway through International Dark Sky Week, Bettymaya Foott is leading about a dozen people through downtown Salt Lake City after dusk.

Foott works with the Colorado Plateau Dark Sky Cooperative. It aims to preserve views of the stars in the night sky by cutting down on light pollution.

“Light pollution is defined as any negative aspect of artificial light at night,” she says.

Foott says light pollution can have impacts on wildlife, energy costs, and health.

It includes what’s known as an urban skyglow, or the haze of light around cities that obscures the stars. But it also includes things like the glare of streetlights through a bedroom window. Last year the American Medical Association confirmed that LED street lighting can disrupt the human sleep cycle.

“It definitely affects sleep and insomnia, but it’s also been linked with rates of breast cancer, prostate cancer, diabetes and obesity,” Foott says.

Utah leads the nation with nine certified dark sky parks, which means exceptional stargazing.

But the Salt Lake Valley’s skyglow is visible from the other side of its surrounding mountains. So Foott organized a walk through downtown to learn more about the light sources around the city.

She points out decorative light fixtures that point straight up into the sky, which the group describes as “useless,” and windows into empty office buildings with the lights left on.

“I’m sure not everyone in these offices is working, right? The lights are probably just left on,” Foott says. “And they can save a lot of money by turning these lights off.”

The group stops in front of the Harmons grocery store to look at the lighting above its loading dock.

“Fully-shielded directional lighting, appropriate for the task, not obtrusive to our eyes,” Foott says.

She delivers the final verdict: “Good job Harmons.”