NEW YORK – New York pedestrians tend not to look up too much for fear of being mistaken for tourists gawking at skyscrapers. Ian Cheney gazed toward the heavens and got a film out of it.

Cheney’s documentary, “The City Dark,” is an unexpected walk through the implications of well-lit cities. It airs Thursday at 10 p.m. on PBS, part of the “POV” film series that is marking its 25th season on the air this year.

The filmmaker, who grew up in rural Maine and has lived in Brooklyn for three years, noticed how few stars he could see in the night sky above the city because of nighttime lighting, certainly compared with what he was used to.

“It was surprising when I came to realize how much it was affecting me, how much of a sense of loss I felt,” he said.

He pointed his camera upward. Cheney’s original idea was to explore what the disappearing night sky meant to astronomers who had to search for more remote locations to get clear views for their telescopes. He found astronomer Irve Robbins, who runs an observatory in Staten Island, who said, “I’ve seen the Milky Way twice – when there were blackouts.”

Cheney’s research took him to interesting new places where urban lighting had unanticipated consequences.

For generations, sea turtles that hatch on the beach in Florida have instinctively sought out the starlit horizon of the ocean and headed for water. Now, thousands are being confused by glowing skies from artificial light and are heading the wrong way, and don’t survive.

A scientist in Chicago showed Cheney file cabinets with thousands of bird carcasses. The migrating birds had become confused by city lights and slammed into closed windows, killing themselves.

He talked to Suzanne Goldklang, who worked an overnight shift in a well-lit television studio selling jewelry for a shopping channel. She has breast cancer and has learned about research that is finding people who work night shifts exposed to a lot of artificial light face an increased cancer risk.

The film reflects Cheney’s personal journey making it.

“Many times you start out with a script and just fill in the blanks,” he said. “In this case, I had to shoot a lot of footage because I didn’t know what direction it was going to take.”

Reminiscent of the early conservation movement, excessive nighttime lighting is quietly becoming an issue in many communities where regulations are being passed to curb the practice. After one was passed in Bar Harbor, Maine, Cheney’s parents (who live in Waldoboro, a few hours south), installed a cap on a security light outside of their barn so the light was only reflecting downward.

“I came to realize that light pollution represents an insidious danger to our society,” he said, “not one that makes buildings fall down or leads us into immediate financial ruin, but one that affects us culturally and spiritually in ways that I thought were important to explore.”

Cheney isn’t a polemic, and neither is his film. He’s surprised at people who suggest that his goal is to turn off the lights.

He loves a sky full of stars, but also appreciates the beauty of a city skyline at night. “The City Dark” visits a neighborhood made safer by lighting and includes an interview with the designer of a New York park who is trying to balance offering enough light for safety but not enough so it looks like daytime at midnight.

“We so clearly need good lights for navigating and safety and beauty and art and architecture,” he said. “It’s just a fallacy that we can’t have well-designed lighting and a darker night sky.”

Cheney’s hope is that his film will encourage people in cities to consider issues they may not have thought about before.