The average amount of sleep one needs to remain healthy is 7-9 hours of consistent, unfragmented sleep. When I was an undergraduate college student, I worked as a Sleep Disorders Technician for 5 years to finance my college education.
If you want to learn more about sleep, check out these books:
Principles and Practice of Sleep Medicine
http://www.amazon.com/exec/obidos/t...f=sr_1_1/102-3012465-6993717?v=glance&s=books
Principles and Practice of Sleep Medicine in the Child
http://www.amazon.com/exec/obidos/t...f=sr_1_2/102-3012465-6993717?v=glance&s=books
Treating Sleep Disorders: Principles and Practice of Behavioral Sleep Medicine
http://www.amazon.com/exec/obidos/t...f=sr_1_3/102-3012465-6993717?v=glance&s=books
It's very important to get the same consistent sleep (same time of the night, no staying up late one night, then going to bed earlier another night), unfragmented sleep. You'll live longer, feel better, and function better through out the day.
Your circadian rhythms are governeed by several feedback mechanisms. It's important to be exposed to natural sunlight to produce meletonin, a hormone critical for good restful sleep. Fluorescent lighting will not stimulate the production of meletonin (bummer for people "inside" all the time). During the first 4 hours of sleep, neurotransmitters and much protein synthesis are taking place (delta sleep). The latter four hours of sleep have increased REM (dreaming) that is important for learning and problem solving.
Not getting the proper amount and QUALITY of sleep will shorten your life time. When you don't get good consistent sleep, you're straining the brain and body, causing irreversible damage. Though it's not much, cummulatively it takes it's effect. This is why working night shifts, or rotating shift work shortens the life time 5 to 10 years.
Well, read up and enjoy.