system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do our eyes see 'noise', like high ISO photos in dark rooms?

It has the same effect but only a little less colorful.
gpt
Imagine you're in a crowded, noisy auditorium. You need to shout loudly just to talk to the person next to you. Even when the speaker goes up to the podium, they can't be heard above the noise of everyone speaking. However, once the speaker gets everyone's attention, everyone starts to quiet down until it's silent enough that everyone can hear the single speaker talking.

The same thing happens in our eyes. Our eyes are capable of looking at a extremely wide range of brightness from direct sunlit days down to moonlit nights. While we can quickly adjust from going from dark to light, our eyes have the downside that going from light to dark takes a long time. 

When our eyes are adjusted to light, a percentage of the chemical sensitive to light (rhodopsin) is getting recycled. This recycling can stimulate the nerves that see light, providing the noise in the auditorium. If something is bright (loud) enough, you can notice it over the noise. However, when there is nothing bright enough (if you go from a bright environment to a dark one), you just notice the "noise" from the chemical recycling which can look like noise from high ISO photos. This appears to us in black and white because our most light sensitive photoreceptors in our eye can only sense brightness, not color.

After about 15 minutes, the light sensitive chemical recovers completely, resembling the time it takes to quiet down a noisy auditorium. Now, your eyes are the most sensitive to light. There still may be some noise since the blood flow through your eye can accidentally cause enough pressure so that the light sensitive cells think they see something. This also contributes to the noise you see in darkness.