morning sunlight x cortisol x sleep - 60 days of tracking

10-15 min of outside light in the first hour of waking, tracked vs evening sleep latency + HRV. consistent effect. no light = took 30+ min to fall asleep + HRV worse. with light = under 15 min + HRV up. it is apparently free. i resisted it for years because it felt like influencer advice. it is just physiology.