When telling my Dad about natural light exposure first thing in the morning this week I noticed Dr Huberman recommends ≥5 min when it's sunny and ≥15 min when it's cloudy I'm going to start running in the morning again instead of the afternoon on cloudy days. It's more enjoyable for me than standing outside for 15 min, especially when it's cold. https://www.hubermanlab.com/newsletter/using-light-for-health#:~:text=On%20a%20sunny%20morning%2C%20get%20outside%20for%205%2D10%20minutes