On a quiet block in downtown Brooklyn, a new photography exhibit — housed inside a senior living center — invites viewers to consider an essential question: How do we measure the emotional and social costs of discrimination?

The exhibit, “Not Another Second,” shot in 2019 by a German photographer, Karsten Thormaehlen, profiles 12 older adults who identify as L.G.B.T.+ (the “Q” is deliberately missing because the word “queer” was often used as a pejorative term against the people profiled), through a series of portraits and video interviews.

Almost all of them spent several years of their lives hiding from prejudiced eyes, even to do the most normal of things — to walk with heads held high, to live without being considered crazy, to serve in the military, to marry their lovers, to hold down jobs.

It has, after all, been less than 50 years since the American Psychiatric Association changed its view of homosexuality, stating that it should no longer be considered a mental “disorder”; 10 years since the military’s “don’t ask, don’t tell” policy was repealed; and almost six years since the Supreme Court declared same-sex marriage a constitutional right.

Together, that’s about 65 years of slow change. Or, one lifetime.

Accompanying each profile is the number of years that person lost before coming out.

Collectively, the group of 12 lost almost 500 years.

One gay couple, Ray Cunningham, 83, and Richard Prescott, 79, talk in a recorded video about growing up in the 1950s and ’60s. At one point, Mr. Cunningham looks into the camera and explains how, when he was a 19-year-old Navy man, he was in charge of giving his gay colleagues “undesirable discharges.” He chokes up, his lower lip quivers. He came out to his mother when he was 21 years old and never came out to his father.

Mr. Prescott recalls how, when he was a high-school senior, he was called out by one of his classmates for always looking down at his shoes when he walked around campus. That, Mr. Prescott explains, was a defense mechanism. “You just, you don’t look up,” he said. “I mean, you don’t want to face other people that you feel are going to reject you.” He came out at the age of 60.