I started using one of these this year, and it's working well, but not in the way I expected.

I expected that: the light would wake me up, and it would be nicer than an alarm.

In actuality: I wake up often in the early morning anyway, and normally I roll over and go to sleep. If I happen to wake up in the 20 minutes when the light is rising, I don't go back to sleep, I just get up instead.

Result: the light isn't "waking me up", but I awaken "naturally" most days because of the light anyway.