Under normal circumstances adults sleep 6-8 hours at night is the best, the elderly need to increase sleep time on top of this, the elderly recommended to sleep 8-10 hours a day to best, children should sleep 10-12 hours, infants and children can be in 12 hours longer are the best sleep time. But there is a prerequisite that for adults, the deep sleep phase should be greater than 4 hours, and the sleep phase should be less than 3 hours to achieve the best sleep quality. Therefore, the best number of hours to sleep at night is not the number of hours, but the number of quality of sleep, as much as possible to shorten the phase of light sleep and increase the phase of deep sleep to be beneficial to the body, the best effect on physical fatigue and recovery.