Why isn't the dark ... dark?

There is probably some light coming in from outside.

When you turn off the lights it might appear pitch dark, but as your eyes adjust, if you cam see, there is light coming from somewhere. Does that happen when you wake in the middle of the night? You can see somewhat? And then if you ut on the light amd turn it off again it is pitch dark for you again, and you can’t see as well as when you first woke? Or, can’t see at all?

The light was probably from outside, and just enough to come in the window.

What you’re “seeing” is the random firing of your retinal ganglion cells. These are the cells that process the information from the photoreceptors in your retina and translate it into impulses to be transmitted along the optic nerve. Even in the total absence of light, the ganglion cells keep up a steady, low-level firing that you see as this faint light static in the darkness.

What @thorninmud wrote.
In the absence of actual light our visual systems make stuff up.
This sort of background neural activity inspired early sensory deprivation chamber studies to see what does the nervous system sense when there is no external input.

Sometimes when I first close my eyes to go to sleep, I can see images. I used to see abstract patterns. Lately it has been people’s faces. It is not a dream or an hallucination. I am completely aware that these are pure fictions.

There is a lot of light pollution in civilization. I lived on an island where most of the residents were only there in summer. It was pitch black dark at night. But the sky was magnificent.

We are thermodynamic systems running electrical circuits. Like all well developed I/O devices, our input stages have AGC (automatic gain control) that ramps up our input amplifiers so we can detect low level signals. The response time for the AGC depends upon the input device but is usually in the form of an RC time constant . If no signal is detected the AGC will increase the amplifier gain until some noise floor level is reached and we are at our most sensitive. That’s why we can detect an ant crawling on our skin or the sparks our sheets make when we slide our hand over them in the dark.

And what @thorninmud said.

@marinelife Ohhh how I miss looking up at the sky and being able to see the milky way band across the night sky.

@LuckyGuy So, does that explain why the TV sounds so ridiculously loud when we fall asleep with it on and wake up in the middle of the night? It’s not the TV station; it is our senses that are amped up.

Our sense of touch and its sensitivity decay function is a vestige from when we branched from reptiles.

Hearing has a noise threshold that increases as we get older. Tinnitus.

Our sense of sight has an incredibly large dynamic range. We use the retina’s rods to go to “dark adapted mode” or scotopic vision if we want to see in near total darkness.
In total darkness you can even “see” get a flash if your eye is hit with a radioactive particle – or even a microwave burst. Don’t try this at home but an IR pulse to the side of the head can also induce a green image. (Litigation is continuing.)

We are all uncalibrated sensor modules.

It has to do with your eye perception. The color, a very dark grey, is called Eigengrau.

Hmm. I visited a disused coal mine in Pennsylvania that is now open for tours, and while the group was down there the guide turned off all the lights. That was a darkness deeper and more entire than anything I could remember ever experiencing before. It almost felt solid, like a wall. And it sure didn’t seem to me that there was any sort of gray tone or random firing going on. It seemed too dark even to be called black.

@Jeruba I know what you mean. I have been in total darkness and it is very odd. I described it as thick, but wall works for me too. I feel afraid to move in it.

@LuckyGuy I have much more trouble than everyone else I know adjust from darkness to light. I sometimes wear sunglasses to watch TV in the middle of the night if I wake up.

@JLeslie I’ve experienced that in some caves in Belize.Total and utter darkness and complete silence. I found it to be a very relaxing experience.

Ambient light from somewhere ! The dark is nothing more than the absence of light but without light your eyes would see nothing. So there was some light where you were at or there would have been no sight!