Macroscopic signals like morning light, characterized by long and short wavelength contrasts (orange-red blue contrast), inform the brain that it is morning.

“these um kind of macroscopic signals like light coming in in the morning has these you know long wavelength and short wavelength contrast that's what tells our brain it's morning that's right it's the orange red blue contrast even if there's cloud cover it's the it's the difference between those to um different qualities of light that says it's morning”