I plan to explore this more fully this summer when the dry season hits. (We're in an El Nino pattern this year, so I should have plenty of cloudless days this summer.)
Robert Barefoot discusses a number of biochemical actions which occur as a result of direct sunlight -- both within the skin and within the various glands behind the eyes -- in The Calcium Factor. If you want some Science behind your spirituality, that might be a good place to start.