An article from the New Yorker by Maria Konnikova has an interesting introduction to the concept of sleep inertia. The time between the moment you wake up in the morning until the moment you are really awake is called sleep inertia. And it can be really bad. It turns out that our brains take some time to get into awake mode, and as a result our memory, and ability to perform are negatively effected.
There’s a good quote from Professor Kenneth Wright:
Cognition is best several hours prior to habitual sleep time, and worst near habitual wake time.
So if you have a mission critical activity, you’re going to want to minimize sleep inertia. To do this, you’ll want to wake up naturally. And that’s affected by natural light, and your own internal alarm clock. We can each appreciate that our bodies are very different, so each person will need to emperically determine the best sleep habits. And contrary to what your mother may tell you, sleep duration doesn’t necessarily lead to the best outcome.