> According to recent studies, obtaining more daylight during the day, as early risers do, triggers a chain reaction of hormonal changes that might affect mood.

I think this is the key is the daylight, not the regular amount of light, but the strong brightness in the early morning that trigger hormone affects not only our mood but our immune system as well.

Personally, I don't think it's related to a sleep schedule. it's more about the light. I've been recently listening to the Andrew Huberman podcast. He's a neuroscientist and has a weekly episode. And in one of his episodes, he mentioned that regular human being needs to be exposed to sunlight at least 30 mins a day. Not just a light, but the strong brightness coming from the sun which triggers hormones increase our alertness by raising the amount of cortisol in the body.

of course, this means more productivity, more immunity, and controls the mood. There's another way to do it, an ice bath for example but the light is actually more important than we think.