Too often, these prisoners are “maxed out,” meaning they are released from solitary directly into society. In Colorado, in 2012, 140 people were released into the public from Ad Seg; last year, 70; so far in 2014, two.

The main light in my cellblock eventually turned off, and I fell into a fitful sleep, awakening every time a toilet flushed or an officer yanked on the doors to determine they were secure. Then there were the counts. According to the Ad Seg rules, within every 24-hour period there are five scheduled counts and at least two random ones. They are announced over the intercom and prisoners must stand with their feet visible to the officer as he looks through the door’s small window. As executive director, I praise the dedication, but as someone trying to sleep and rest my mind — forget it. I learned later that a number of inmates make earplugs out of toilet paper.

When 6:15 a.m. and breakfast finally came, I brushed my teeth, washed my face, did two sets of push-ups, and made my bed. I looked out my small window, saw that it was still dark outside, and thought, now what?

I would spend a total of 20 hours in that cell. Which, compared with the typical stay, is practically a blink. On average, inmates who are sent to solitary in Colorado spend an average of 23 months there. Some spend 20 years.

Eventually, I broke a promise to myself and asked an officer what time it was. 11:10 a.m. I felt as if I’d been there for days. I sat with my mind. How long would it take before Ad Seg chipped that away? I don’t know, but I’m confident that it would be a battle I would lose.

Inmates in Ad Seg have, of course, committed serious crimes. But I don’t believe that justifies the use of solitary confinement. My predecessor, Tom Clements, who was as courageous a reformer as they come, felt the same way. Mr. Clements had already gone a long way to reining in the overuse of solitary confinement in Colorado. In little more than two years, he and his staff cut it by more than half: from 1,505 inmates (among the highest rates in the country) to 726. As of January, the number was down to 593. (We have also gotten the number of severely mentally ill inmates in Ad Seg down to the single digits.)

But Mr. Clements had barely begun his work when he was assassinated last March. In a tragic irony, he was murdered in his home by a gang member who had been recently released directly from Ad Seg. This former inmate murdered a pizza delivery person, allegedly for the purpose of wearing his uniform to lure Mr. Clements to open his front door. A few days later, the man was killed in a shootout with the Texas police after he had shot an officer during a traffic stop. Whatever solitary confinement did to that former inmate and murderer, it was not for the better.

When I finally left my cell at 3 p.m., I felt even more urgency for reform. If we can’t eliminate solitary confinement, at least we can strive to greatly reduce its use. Knowing that 97 percent of inmates are ultimately returned to their communities, doing anything less would be both counterproductive and inhumane.