why do your eyes adjust so fast to bright light but so slowly to darkness?
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Your pupils clamp down quickly because very bright light can damage your eyes. Kinda an “emergency lockdown” situation.
They can expand more slowly to be cautious of overdoing it.
Your eyes have to adjust quickly to bright light to prevent damaging them. That’s why going from a dark room into bright sunlight hurts your eyes. Adjusting to darkness takes longer because there’s no I’ll effects to it being slow to your vision.
Your eyes contain 4 different types of light sensors. The first 3 see color and the 4th sees shades of gray.
In order to “respond” to light, the sensors use chemicals that interact with the light *color* they see. So chemical X responds to Green colored light, chemical y to Red and chemical Z to any light, but only responds in shades of gray.
Long story short, the gray chemical, chemical Z gets destroyed by bright light, any kind of bright light melts it away and your eye needs to build more up before you can see gray-scale.
So if you’re in bright light and then suddenly go into the dark, you have no chemical Z and it needs to restore over a short few minutes and then you can see in the dark at least a little bit.
Fun Fact: Red light does NOT destroy chemical Z. This is why military aircraft and vehicles that operate at night use Red lights in the cabins before dumping the soldiers off into a battlefield. You can leave the vehicle with full night vision intact.
Adjusting to bright light is different, a muscle in your eye just squeezes the eye-hole tighter reducing the amount of light that gets through into your eye in the first place. It happens pretty dang quick.
There are molecules in your eyes that undergo chemical reactions when light hits them. Those chemicals are responsible for the eye’s sensitivity to light. It takes a while for them to transform back to their original state. The reason for the difference in speed is because it takes a while to go from daylight to darkness so during that time your eyes would slowly be adjusting to the change in the amount of light until it was completely dark and you went to bed. At which point you’d wake up and it would be mostly light out again and you’d need to be able to see right away.
This error be evolutionary good. It’s much more dangerous leaving a cave than entering it (assuming you know there’s nothing dangerous in the cave).
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