[gambiting]

It would just be....completely dark? I had this experience when working at a mine at one point, and if you went down one of the tunnels and switched off your headlamp.....it was absolute darkness. Like, we think that our bedroom at night is "completely dark" - but that's usually not true, that's always some source of light, after some adjustment you can see at least faintly. In an underground corridor without any lights at all it was very uncomfortable, it was like completely losing one sense of perception entirely.

[ericjang]

That reminds me of the flavor text of this Magic the Gathering Card (https://gatherer.wizards.com/pages/card/details.aspx?multive...)

There's an experience worse than blindness—it's the certainty that your vision is perfect and the horror that there's no world around you to see.

[bdamm]

Pilots flying in "hard" instrument conditions also experience this. You can see the interior of the airplane, but everywhere you look outside is exactly the same shade of grey/black/white, and there's no usable data from your sense about the position of the airplane relative to the earth. Passengers who think about this might intellectually get it, but it's quite a different experience when you're looking out the front window and responsible for choosing the correct control inputs. I believe scuba divers diving at night also can experience this.

[justinclift]

When night diving, you can at least blow air into your hand then feel which way the bubbles travel. eg "which way is up?"

[julienreszka]

Unless you have a closed system like special forces usually do

[newnewpdro]

I think they meant an illuminated room, but with absolutely no light being reflected by the wallls/floor/ceiling etc.

So all the visual spatial cues would be missing, despite being illuminated, like being in an infinite space. I could see how that might be disorienting and strange feeling.

[elihu]

Even well-lit caves (or similar environments) can be disorienting. A few years ago I was walking in a sandy-floored lava tube with a flashlight, and the floor was sufficiently uniform and featureless that I didn't have a clear sense of depth perception.

Another time I was flying a radio-controlled glider at the beach on a foggy day. There was a big rock sticking up in the middle of the beach. I thought the glider was closer than the rock, but then suddenly it vanished from sight because it was actually farther away and went behind it. Another flight I thought I was about 20 feet off the ground and then it suddenly struck the sand and slid to a stop.

[watersb]

Flying over water can be dangerous, as it is often impossible to judge distance to the surface, even for experienced pilots,

[topspin]

I've actually worked on blocking all light in one bedroom. This is a great thing when one must sleep during the day.

The one window is thoroughly covered using well fit light blocking material. During daylight there is a very small amount of light the gets in under a door. At night it is utterly black. You may wait as long as you wish for your eyes to adjust; you cannot see your hand in front of your face. Nothing. Activating a smart phone becomes painful.