Our bodies work on 24-hour circadian rhythms, so viewing the sunshine concurrently daily allows keep the inside clock in sync. (On cloudy or rainy days, filtered daylight will however have an impact.)
Caffeine and https://www.facebook.com/econopass/posts/pfbid0AEX1p1FDnrm5AKwdR1sDtkp1mx3yQQ1Naa9JT9FQjQTpYZBoHdgdPaX72Qr52GE4l