Why do we sometimes see random patterns or colors when we close our eyes?
In: Biology
These are called phosphenes. TLDR: your eyes aren’t perfect, so sometimes they send incorrect signals to your brain. Your brain isn’t perfect, so sometimes it imagines signals when the line goes quiet.
**Slightly longer version below:**
In the back of your eye, you have a bunch of cells called your retina. Your retina normally takes in light and converts it to an electrical signal. This process can continue even when the light stops.
For example, if you look at a bright computer monitor for a few minutes, you’ll still see some outlines of that monitor when you look away. This is called an [afterimage](https://en.wikipedia.org/wiki/Afterimage#:~:text=Afterimages%20occur%20because%20photochemical%20activity,longer%20experiencing%20the%20original%20stimulus.).
In addition, any biological system has some “noise” (aka random error). With your eyes open, the error rate is really low and faint; you generally won’t notice it compared to a brightly lit view.
Your cells are more likely to misfire in the dark, because fewer cells are being activated. You’re also more likely to notice it in the dark.
Those cells can also be forced to trigger by some factors like low blood pressure or if you rub your eyes aggressively (don’t do that, it’s not good for you).
This could also be caused on the other side, in your brain. When a nerve system goes dead (for example, if your eyes completely stop sending signals), your brain is usually still expecting a signal. It can over-interpret anything sent to it because its biased toward seeing meaningful signals.
This could cause you to feel a limb that had been cut off, hear noises even if your ears are deafened, or see random patterns if your eyes are closed.
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