8 hours of sleep can make you happier - plus 21 other discoveries from sleep-tracking devices

Sleep. We can't live without it and we can't function without enough of it.

But for most of us, getting enough sleep is a problem.

40 million Americans each year suffer from chronic sleep disorders and an another 20 million experience occasional sleeping problems, according to National Institute of Neuroligical Disorders and Stroke.

But thanks to fitness trackers like Jawbone UP, and sleeping-aid apps like Sleepio, we have all sorts of data on how we sleep and how to improve our rest.