It turns out that not sleeping in complete darkness can affect your sleep/wake/cortisol cycle and actually promote weight gain! Although this study was performed on mice, I think the results are at least a little applicable to us humans.
The more gray hair I get (signs of wisdom, right?) the more it seems to me that in order to be happy and healthy, we should try to reproduce the conditions that humans have been living in for the past ten thousand years. (or one million years, for you evolutionists out there) Eating the same types of natural foods, getting the same intermittent, vigorous types of exercise, and now sleeping in complete darkness, just like our ancestors...
Of course I don't want to live in the woods and sleep with the bugs, but I don't want to gain weight just from the overly bright glow from my bedside alarm clock either! With all our efforts to eat a better diet, and get more exercise, I'll be damned if I'm going to "plump up" just because I forgot and left the bathroom light on!
Here is the Study that shows that mice exposed even to dim light during sleep hours tended to gain more weight. Turning off all the lights (and TV!) and putting thicker drapes on the bedroom window could actually help a little in the quest to lose weight, not to mention sleeping better. It might take a few nights to get used to this new dark sleep environment, but the savage in you will be thankful that you did. If you need a little help getting to sleep in this new environment, here is what I recommend.