I have a curious non-problem that occurs to me at specific times, and was curious if this is common for everybody or what. Hopefully I can convey it well enough.
As background, I have poor eyesight. Without my glasses I have trouble distinguishing anything more than a foot from my eyes. I have something like 20/200 vision in my good eye. I am not colourblind in any fashion.
Now, whenever I am in a low-white-light situation, or no-light and my eyes have adjusted, such as at night or the period near dawn when a little light is coming in through my shaded windows or being in a bathroom with the light off, something curious occurs. Or maybe it’s not curious, you guys can help with that. When this time period is met, I lose my ability to distinguish shapes, as if I had my glasses off. That and the little white and black minisparkles that occur when you rub your eyes are constant and over my entire field of vision. I can figure out what things are, and they’re not as fuzzy as without my glasses, but I may as well go without wearing my glasses in this time. I can see how this is likely, as there’s not enough light to delineate objects.
That’s not all though. I lose my colour perception too, achromatopsia-style. I figure this is a lack of light again, but talking to relatives and friends, they can’t figure out what I’m talking about, so maybe they don’t have it. Everything ends up greyscale. I look at my yellow sheets and wow they seem to be the equivalent of blue in my greyscale. Tie-dyed clothes will seem to be uniformly coloured in some patches. I can only tell when similar-coloured objects begin and end due to slight shadows. A light blue object on my yellow sheets will seem slightly darker, but the sheets will still seem to ‘appear’ blue (there is no ‘blueness’ to them, but the grey I can see just seems to correlate to a medium/light blue). I can still perceive colour IF I look at something that is colour-lit. My alarm clock’s red LED numbers are red. If I have a slightly orange nightlight, things in the illuminated area will be properly coloured, but nowhere else.
This all makes sense with not having enough light, but is it really supposed to be that way? Can other people see colours when it’s mostly dark?
Sounds right to me. Your eye has two types of photoreceptors, rods and cones. The rods are more numerous but aren’t sensitive to color, and the cones are sensitive to color but are less numerous and less sensitive to light in general. So color perception suffers in dim light.
It may be the case that your really awful vision accentuates the effects of low light on your color perception, possible because of the large eye dilation.
The lack of focus at low light can be due to the dilated pupils. In bright light the pupils contract. Given the same out-of-focus lens, using a smaller aperture reduces the size of the blur and sharpens the image. That’s why squinting your eye helps. You can also make a tiny hole with your finger and look through that - you’ll see a much sharper image. In dim light your pupils are dilated all the way so you get the maximum blur. If you have a perfect lens it shouldn’t make a difference, but you probably don’t have 20/20 vision even with your glasses. I certainly don’t,(barely enough to get a driver’s licence in fact) and I have noticed the same thing.
That does remind me, I’m ultra-sensitive to bright lights. My opthamologist said the backs of my eyeballs were ‘pale’ and said that was why I suffer severe pain when exposed to bright sunlight. So I can see fairly well in the dark, at least I switch to dark-vision very quick. Maybe that has something to do with the severity too?
A cool thing I noticed a while back on the same topic: I was spending a lot of time staring through a spotting scope, so I put a patch over the eye I wasn’t using. When I took off the patch, there was this grey line about an inch wide along the (reddish) soil. It turns out this line was where the leg of my tripod blocked the sight from the un-patched, and therefore light-habituated, eye, so I was seeing that strip of soil with only the dark-adapted eye that had been patched, and seeing it without colour perception. This kinda freaked me out so I dug deep into the recesses of first-year-undergrad-bio memory and fashioned an explanation that reassured me I wasn’t doing any permanent damage. I have no idea how ``correct’’ it is beyond that, though, but here goes:
As far as I recalled, there are two responses to bright light: one is closing down the aperture (the pupils, if I’m using the right word…), which is fast and reduces the amount of light getting to the active bits. The other is chemical and has to do with how many photons need to hit a rod/ cone cell before it fires off a nerve impulse, and takes longer to act. So my guess is that in adapting to lower light behind the patch (actually attached to the scope, so not blocking all the light by any stretch), the pupil dilated and the chemical response favoured the not colour sensitive rods. Then when I looked up, the pupil contracted immediately, and this was enough to cut down the number of nerve impulses sent (by cutting down light), so it didn’t feel painfully bright. Then gradually (my guess is 20-30sec), the chemical reactions lowered the sensitivity of the rods and the pupil dilated again, allowing the cones to start picking up colours, but keeping the average nerve impulse rate the same, so I did not perceive any change in brightness.
Cool effect, and nicely explained by a hypothesis I constructed to fit it based on what I remembred. Someone here may elabolate on the hypothesis if they feel inclined and qualified…
Another difference between the rods and cones: the cones give visual acuity (sharpness), while the rods are better at detecting motion. This is why you sometimes see a flicker at the corner of your eyes, but can’t spot it when you look at it directly. This is the effect of flourescent light that bothers many people, especially in places that use 50-cycle AC power. The flicker is apparent in your peripheral vision (the area populated primarily by rods) but not in your primary focus (the area populated with the highest concentration of cones).
Along the same lines, your color perception fades at the edges of your vision. You can’t tell the colors of objects in peripheral vision.
(Note that if you try this, you must control carefully. The eye darts around constantly [5 times/sec] to cover the whole visual field, and your brain is very good at guessing what’s there. Have a friend hold up a colored pen or something and gradually move it into the field of vision until you can detect it, then try and guess what color it is.)