system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why we don't see full black in night/close eyes but see random noise moving around?
gpt
I suppose it could be visual snow, but more likely what you're seeing is called eigengrau.

To explain, the way your eyes see in dim light is for particles of light to enter the eye and strike the rods of the eye, specifically activating a protein called rhodopsin. This protein is extremely sensitive to light, which enables us to see in very dim light, but is also so sensitive that it can be activated by the heat of your body. Since, even in pitch black, some of this rhodopsin would be activated by the heat of your body, you see a dark grey when you close your eyes instead of pure black. When your eyes are open this dark grey is actually the darkest color you can see, your brain just  compares it to the other lighter objects around it and you interpret the object as a pure black.

True ELI5, your eyes can never see pure black because the chemical in your eyes that let you see in dim light is so sensitive they can activate from the heat of your body, making your brain interpret a dark grey instead of a pure black.