A friend would constantly harp on about this guy Dr Jack Kruse, and a saw a Skype interview, was like meh and lost interest after maybe 5 minutes. Then I got his 2 part interview on the life stylist podcast (iTunes link for iphone) from mid 2017. Sold, so now sunlight is a crucial part of my routine. Basically sold on the science, I love it. Early morning sun and sunset, I try to be facing the sun