How do our eyes “get used to the dark”?



How do our eyes “get used to the dark”?

In: Biology

Your pupil dilates, meaning it enlarges and allows more light to enter. It can take a few minutes, but once more light is allowed to enter, you’re able to see more.

If you shine a bright light on someone’s eye, you’ll see the pupil quickly shrink.

Fun fact, pirates wore an eye patch because it meant when they went from the bright deck to the dark inside, they would have one eye already adjusted to the dark so they wouldn’t be blind for a few minutes while their eyes adjust.

Edit: I am not entirely correct.
a)The pirate thing appears to be based on zero evidence. Apologies for propagating a myth.
b) pupil dilation is a seconds long process, and only part of the story when it comes to night vision.

Your pupils (the dark circle in the middle of your eye) dilate, taking in more light, so you take in more information! Really simple as, I hope I didn’t get anything wrong

Your rods in the retina which detects light and dark do this by constantly producing a chemical which gets broken down in light and then measure the amount of chemical in the cell. In bright light there is very little chemical in the rods but there is still a lot of variation so you will notice it, in fact in bright light most of the vision is based on the cones which works similarly but are sensitive to color as well. However when you go into a dark place there is still very little chemical in the rods but now the light is not strong enough to break it down. You need to wait for the level of the chemical builds up enough that the light actually have a significant impact on the amount of chemicals. And this takes time. It can take up to an hour to get full night vision and you are able to see clearly in a moonless night. However most of your vision will be restored in just a few minutes.

Light dims more and more, then eyes go “Can’t see very well, want MOAR light” and then pupils dilate to try and take more light in so you can see better in areas with poor lighting.

Your pupils, the black part in the center of your eyes get bigger, when they do this it allows more light into your eyes allowing you to see in the dark better.

Here’s another way of thinking about it:
Imagine you are in a lit room but you have a black blanket over you that doesn’t allow any light through it. You’ll then be in the dark.
Now cut a 1″ hole in the blanket and you’ll get some light, but not much. Now make the hole bigger at 4″ you’re going to have a lot more light coming through and it will be brighter.

The same happens with your eyes, your eyes are very sensitive to light which is why they need to adjust, if they let all the light in all the time it would be way to bright and you couldn’t see anything, if they never got bigger you’d never be able to see in dim lit or dark areas.

The pupil opening is a minor contribution to the overall adjustment, allowing for about a factor of 10 improvement in low light visibility.

The rest of the improvement in night vision is done chemically, by regeneration of photopigments, which increases the sensitivity of the retina, by between 10,000 and 1000,000 times

If you are familiar with cameras, the pupil dilation is like opening up the aperture.
The increased retina sensitivity is like increasing the ISO (but with a huge ISO range available)

[This is the Wikipedia article ]( that discusses eye adaptation

Nighttime is WAY darker than daytime – ten million times darker. Seeing in the day is like measuring the speed of a whole river of light, while seeing at night is like counting drips of it. These are such different problems that our eyes use different cells to solve them.

During the day you measure that river of light with ‘cone’ cells. There are three types with different sensitivities that let you see different colors. During the night, you use ‘rod’ cells that have a delicate chemical mousetrap to catch the little drips of light that come in. Switching to the night vision system takes a while (20-30 minutes or so) because all of those little mousetraps (a chemical called rhodopsin) have been destroyed by the river of light you were just in.

Your eyes also perceive color differently in darkness vs. light. Cones and rods and such. Anyways, this is why film sets are illuminated with, or edited to add blue. It gives the “illusion” of darkness while still allowing the audience to see the action.
If only they’d have used that at the battle of Winter fell. (Still too soon?)