Along with exercise, feeding and social interaction when and how you view light has the strongest influence over your level of alertness, mood, learning, and your ability to fall (and stay) asleep at night.
Fundamentally, your body is a 24-hour factory and for it to function well it needs to know the time of day, and one way the brain works this out is by measuring the intensity of light hitting the eyes.
Viewing light in the wrong way can screw up your wake/sleep cycle (e.g., it’s 11pm and you want to go to bed, but your body thinks it’s 9pm so you struggle to fall asleep) and can impact mood and learning.
For a bunch of reasons this is bad news, so being healthy should include light viewing habits that keep you synced up to the current day/night cycle.
Viewing light in the morning catapults your body into the day, and is critical for sleep because your body will start winding down for sleep 14-16 hours later.