Yep, our circadian rhythms are disrupted by artificial light, which is a whole lot weaker than natural sunlight. The sun gives our body the cue that it's daytime, and lack of the sun means it's night time, and soon time to sleep (melatonin the sleep hormone is only produced in the absence of light). Our sleep systems work better with sunlight, exercise, paleo foods that don't rollercoaster our blood sugar, and a lack of stimulants and depressants like coffee and alcohol.
I find that when I sleep with my curtains open, the sun can wake me up pretty well, without the grogginess associated with many people. I can do pretty well with 6 hours of sleep, but I don't do any exercise either (which I am soon to change).