Enough sleep is the amount of sleep that allows you to wake up without an alarm clock.

NPR: Excerpt: 'Delivered from Distraction'

In my case, I stuck with an alarm clock app that offers soothing wake-up calls and nerdy charting features that make for interesting water-cooler talk "My REM was so on last night!"

WSJ: High-Tech Sleep Aids: The Tech to Get Some Z's