why do things look dark after you stare at something bright (like a lightbulb)?
In: Biology
Are you referring that after you look at something bright, that shape stays in your sight and everytime you blink you can see it clearly and bright while the rest looks darker?
Im interested too, I always thought it had to be with the light recieving cells having some kind of memory due to their light sensitivity.
In addition to changes in your eye as described in other comments, your brain is fantastically good at adjusting to varying light levels. Think of it as turning up the gain when you are in a dark situation. Not many people realise that even a well lit room is something like 1/10th as bright as a cloudy day outside. Your eye and mostly your brain adapt amazingly well to these changes to the point where you barely notice them, but the adaptation takes time.
There are two reasons why. First, the iris, the coloured part of your eyes, will expand or contract to make a different sized opening based on the amount of light available. Our vision works best with a certain amount of light getting into our eyes, with too much or too little not working as well, which is why we have this feature to control the amount of light that gets into our eyes. You can see this in a mirror, if you have a light source you can switch on and off and a mirror you can put your face close to. [A page that describes this in more detail.](https://learning-center.homesciencetools.com/article/eye-and-vision/)
Second, the layer of cells at the back of your eye in the retina, which the light hits, will sort of “get used to,” or “get stuck” based on what they are seeing. It takes them a short time to recover back to normal. [This causes an afterimage, which you can see by looking at very bright colours or lights for a time and then looking away.](https://faculty.washington.edu/chudler/after.html)
If you can find a mirror you can look at your own eye. You will notice there is a black central bit (the pupil) surrounded by a colored ring (the iris). The pupil is a hole that leads into the dark interior of the eye, the back of which is the light-sensitive part (the retina). The colored ring is a band of muscle which can expand and contract to make the pupil larger or smaller.
The retina needs to be protected against excess light and have access to more light if there isn’t much around. To do this the iris will expand in dim conditions making the pupil larger to let more light in, and in bright conditions the iris will contract making the pupil smaller to let in less light.
When you looked at a light your iris contracted, so when you look away there is less light allowed into your eye and things will look dim.
There is a part of your eye called the Iris that is mechanically similar to your butthole (a sphincter, your body has a bunch of these types of muscles) but it’s purpose is reversed – your butthole (anal sphincter) keeps poop in your butt so you don’t randomly make a mess when there is poop ready to be released.
Whereas the iris prevents too much light from entering your eye and damaging or fatiguing your light and color sensors (rods and cones).
When you go from looking at something bright to something dark, it takes time for the iris to relax. As it relaxes, more light is allowed into your eyeballs which your rods and cones detects.
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