There's been a lot (but not enough) research in this area. There are other factors such as exercise and temperature (so-called zeitgebers: https://en.wikipedia.

There's been a lot (but not enough) research in this area. There are other factors such as exercise and temperature (so-called zeitgebers: https://en.wikipedia.org/wiki/Zeitgeber https://en.wikipedia.org/wiki/Zeitgeber), but light is an extremely strong one for most people.