Today in Sacramento lawmakers are delving into a growing national controversy over special security units that are used to isolate thousands of inmates from the regular prison population. Civil rights groups say long-term isolation amounts to torture while state corrections officials say the units are necessary and the conditions are humane.

Around the state there are four of these facilities, which are known as Security Housing Units. The most controversial is at Pelican Bay State Prison in Crescent City.

At the heart of the debate: conditions in the units (many inmates are held in windowless cells and have been denied everything from calendars and sweatpants to phone calls); criteria that determine which prisoners are placed there and how they get out; and the lengthy terms some inmates spend in the facilities.

More than 500 California prisoners have been locked in the special units for 10 years or longer, according to state data. Of those people, 78 prisoners have been held inside for more than 20 years.

Over the years, authorities have allowed media into Pelican Bay's Security Housing Unit, but access has been limited and the inmates carefully selected by staff.

However, top corrections officials granted unusual access to a team of reporters and videographers from the Center for Investigative Reporting and KQED. We visited all areas of Pelican Bay's Security Housing Unit except for a section housing leaders of a 2011 hunger strike.

Using a small camera mounted to a wall, our team was able to record Beasley exercising with a rubber handball in the small concrete pen (prison staff only began allowing the balls last year). At all other times--day and night—he is held in his cell alone. While skylights allow filtered sunlight into the units, there are no windows.

Producer: Monica Lam
Reporter: Michael Montgomery
Videographer: Singeli Agnew
Editor: Lisa Pickoff-White
Produced by KQED and the Center for Investigative Reporting