For a good health , how long should we sleep ?!

I need about 5 to 6 hours of sleep and will only wake up after 7.30am, nothing earlier than that else will be very tired for the rest of the day and I will look very sleepy, thus could not focus on the things that I am doing. I am more a night person; I do not sleep until it passes midnight every night. I might doze off at 10 of 11 pm but will wake up again, then I will stay up till it past midnight, and I am wide awake between 12am and 2am, most of the time, I will spend my time on the net surfing.

I do not have enough sleep daily because I go to bed late at night. I think that at least seven hours' sleep is needed for a good health. To make up for some sleeping hours, I take an afternoon nap after lunch to gain energy for afternoon and evening work. Have a good day.

I sleep 7-8 hour in normal unstressfull condition and 3-5 hour in exams, I think our body need regular and constant hour of sleeping every day, so sleeping 7 hour at the same time every day make us healthy.