LogFAQs > #922036653

They have done experiments with people where they have done almost this exact thing - stuck people in a room with no clock and no other external clues of time and allowed them to control the lighting to decide when they went to sleep. What they discovered is that people will maintain their sleeping patterns for a few days after the experiment begins then, interestingly, they will naturally shift to a 27 hour rhythm - up for 17-18 hours, asleep for 9-10 (with sleep usually broken up in the middle by an hour or two's wakefulness, which is how our bodies are actually supposed to run and how they did run in the times before artificial light was a thing - the ancient Greeks considered that period to be prime snogging time).