How can you be in a pitch black room, close your eyes, and see grey?

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Why is the blackness of my room darker when my eyes are open than when they are closed? When falling asleep last night in my pitch black room, I noticed that when I closed my eyes there was a grey-ness, instead of the same black that I saw when my eyes were open. There were no prominent light sources in my room and the windows were entirely blacked out. Please explain!

In: 21

I remember hearing or reading somewhere that it is because we actually can see heat, even if mildly, and that’s why when you close your eyes, they catch the heat of your eyelids.

Interesting question! I’m not going to be able to answer it, and I think you struck one that is sneaky-complex, but I’m going to muse for a while anyway. I’m gonna put the comment here, but don’t feel at all obligated to read it!

Remember that our senses are not actually instruments that are giving us readings of the exact state of the outside world. We have photoreceptors in our eye that work like that, but what we see is far more complex than a stream of such data.

If you had rubbed your eyes while sitting in the dark, you would have still seen the colors and light and patterns known as phosphenes as we all do. That’s just your brain and not related to the external world at all.

We’re rarely in truly pitch dark environments. When you are in one, you know it. My guess is that the total lack of light is a pretty different than “a very tiny bit of light in a room anyone would describe as dark”, and that the total lack of data triggers something similar to rubbing your eyes but more subtle. The experience doesn’t fall cleanly into the categories of ‘light’ or ‘dark’ as it is neither. Those experiences are actually on a gradient together and are more similar to each other than either is to “no-data”. I would expect a total blast of light to be sort of similarly free-form interpreted by the brain, but it sure sounds more unpleasant.

To blather on about how what we see is essentially a controlled hallucination generated by our brain:

Remember that photo of the dress that caused such a stir? For many people it looks dark, but for me it’s pretty clearly white and gold. Things like white and gold, meaning the phenomenological experience that I’m referring to when I use those words, do not exist ‘out there’. They only exist inside me, generated by my brain.

A given color appears wildly different in different lighting conditions, so ‘Red’ represents a massive breadth of conditions of the external world. I can see a white carpet in a dimly lit room, and what my eye is seeing is much darker than say a red firetruck in the daylight. But my brain does not get confused about which is white and which is red. One feels the urge to offer the tautological explanation “That’s because white is white and red is red”. But what about the dress?

What we see is our brain’s classification guess about how a given material will behave in varying lighting conditions. That’s what red really is. It’s not out there, it’s in here. Think of iridescence. That’s a word for something that has a physical structure that leads our brains to make an incorrect guess about the color of said object (or rather, a guess that only applies to certain angles).

Our survival depends on it’s relationship to the outside world being consistent, but our vision is not primary data. It is a secondary interpretation. Making accurate guesses about the outside world is the goal of our sense, not the reality. Which is actually pretty obvious when you think about it. Humans do have a tendency to hallucinate at night, after all.

In the case of the dress, it straddles some fine ridge where half of the world’s human brains make one guess about how the material in the photo would behave in different lighting conditions, and the rest make the same different guess. Viola! Dress meme sensation. The dress picture is both light and dark, as those are words for the qualia they spark in humans, which in this case differ. The picture itself, of course, remains unchanged, because our interpretation of it is not a part of it’s essential nature.

I can’t specifically answer your question, but there’s a phenomenon called phosphene which describes how our visual system doesn’t stop working even when denied light.

I would fathom a guess that when your eyes are open in a pitch black room, it may not be as ‘pitch’ as you think, allowing barely detectable light to stimulate your eyes. When you close your eyes, effectively blocking light and creating a truer ‘pitch black’, resulting in the phosphene phenomenon to occur. This might be why it appears ‘brighter’.

But that’s just a completely uneducated guess.

EDIT: Forgot to add that phosphene is the little lights and flashes of colour when you close your eyes. Same as when you rub your eyes, etc.

Also typo.

While I can’t offer a scientific explanation for a 5yo, I can contribute this…

I’ve recently gone completely blind in 1 eye: no light perception whatsoever. And I can tell you that what I see is not black, it’s gray. It’s not affected by light, or heat, or anything…it’s just solid gray, all the time.

My brain actually tricks itself sometimes and I feel like I can see color or light or movement, but when I cover my “good” eye, it’s quickly evident that I am, in fact, still blind.