I've just read something that claimed that in order to be able to fall asleep easily at night (which I can't), you should get exposure to at least 20 minutes of natural sunlight, without glass between you and the light - so no "sunglasses" (according to this article) and no windows between you and the sun. I'm mostly housebound and am worse in the mornings so I don't go outside til the afternoon, if I go out at all. I also wear glasses all the time. If I was sure this claim was legit I might make the effort to get outside in the morning, take my specs off and stare blindly into the distance for 20 minutes, but is this just rubbish? Can anyone point me to some actual empirical research on this?