Light is not supposed to arrive in our system at anytime and now days because of screens and artificial light we have access to light 24/7.
Now we know sunlight within the first fews our waking is great, however the longer we are awake the more sensitive our brain becomes to light, so if you have been awake for say 10 to 14 hours it becomes very easy for even a small of light coming from a screen or from an overhead light to trigger the activation of the clock and make you feel like you want to stay up later and make it harder for you to fall asleep and disrupt your sleeping pattern.
Simple way to think about this is that we want as much light as possible earlier in the day, morning and throughout the day, including blue light and you want as little light coming into our eyes, artificial or sunlight after sunset, DO NOT get any light exposure into your eyes between 11pm and 4am, because light that arrives to the eyes between those times suppresses the release of dopamine (The feel good hormone) and can inhibit learning, it can makes us feel less happy and can leads to forms of depression when we are awake.
Helder, but what do I do if I need to co toilet in the middle of the night?
Simple, go in darkness! DO NOT look at your phone, EVER… If if you dim the screen it will still have the same effect.
If you suffer things like mood swings, anxiety, learning issues, focusing issues, one of the biggest things you can do is take control of this light exposure.
One of the things you can do is to make sure any light in the house are set low, either on a desk or even on the floor, i possible very dim, yellow lights. Do your very best to NOT have any overhead light on.
Candle light and fire places is the best, because it does not trigger the activation of the cells that shift the circadian clock.