The research was conducted by Thomas Wehr, a sleep scientist from the National Institute of Mental Health, and involved 15 men. After an initial week of observing their normal sleeping patterns, they were deprived of artificial illumination at night to shorten their hours of "daylight" – whether naturally or electrically generated – from the usual 16 hours to just 10. The rest of the time, they were confined to a bedroom with no lights or windows, and fully enveloped in its velvety blackness. They weren"t allowed to play music or exercise – and were nudged towards resting and sleeping instead.