Eli5: how is pupillary dilatation almost immediate but “eyes adjusting” to night vision takes a few minutes?

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Title says it all.

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6 Answers

Anonymous 0 Comments

The light sensitive chemicals in your eyes get damaged by light and are constantly regenerated. In bright light they are used up as fast as they are made and there is only a relatively small amount in your eyes. In the dark more and more can build up, which makes your eyes more sensitive. It’s takes around 30 mins for your eyes to “fill” with those light sensitive chemicals, so after going from light to dark that’s how long it takes to get your full night vision.

Little side fact it’s though pirates wore eye patches to save their dark vision in one eye so they could quickly go from bright daylight to the darkness inside the ship.

Anonymous 0 Comments

They take different pathways through the brain. Pupillary dilation is a reflex that takes a more immediate pathway to the pupillary muscles. Think how you reflexively pull away from a hot stove before you even feel the heat.

Adaptation to the dark also requires the regeneration of photopigments in your retina to increase its sensitivity to light, which can take a few hours to fully adjust.

Anonymous 0 Comments

The most basic explanation is that your eyes adjust to darkness in multiple ways. Dilation is just the obvious one, and it happens to be fast as well. The other methods take longer.

Anonymous 0 Comments

Look up “visual purple”. It’s in the retina, responsible for light sensitivity. When your eyes are exposed to light, the visual purple is “bleached”, and takes a while to naturally regenerate.

Anonymous 0 Comments

The chemical responsible for the transition from bright light vision (in colour) to dark-adapted vision (grey-scale) is called Rhodopsin. With bright light hitting the eye, rhodopsin is destroyed and vision is primarily through colour-sensitive cone cells in the retina. In low light, rhodopsin is not destroyed, and vision transitions to rod cells, which are just responsive to light level, and not colour.

The longer you are in the dark, the more rhodopsin builds up to improve night vision.

Anonymous 0 Comments

This is why pirates wore eye patches. Swap the patch even going under the deck. Meant they had a ‘night eye’ and a ‘day eye’