Eli5: Day time vs night time vision

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I learned that felines have (around) 6 times better night vision than us humans. It’s hard for me to get a reference as to how good that is. I thought a good starting place is: How many times better can humans see in the daytime vs the nighttime?

In: Biology

We have different cells in our eyes for day and night vision. The night vision cells are more sensitive but can only do black-and-white. That’s why you need a moment to adjust when the lights are turned off or back on – your eyes need some time to switch from one mode to another.

That’s a difficult question to put a number on I think because day time and night time vision work in different ways.

During the day, lots of light enters your eyes. Humans have lots of cones in eye the which makes us extremely good at distinguishing different colours. Cats have fewer cones so aren’t as good at seeing during the day as humans are.

At night time when there’s much less light, you need rods to be able to see. Rods don’t distinguish between different colours. The reason cats can see much better at night is first, that they have way more rods then we do and secondly, their eyes have evolved to capture more light when there isn’t as much around. You can measure these two things and come up with a number like 6. So if cats have 3 times as many rods and their eyes capture twice as much light, you could say their eyesight is 6 times better.

You can’t really do that when comparing day and night vision because they work differently. During the day, we use rods and cones to see so it’s difficult to put a number on.

If you want to imagine the difference between human and cat night vision. It’d basically be like watching a black and white movie in really low contrast and really low brightness. A cat would be turning the contrast up by 2 or 3 times and the brightness up by 2 or 3 times.

No that is a myth. Their vision is roughly comparable to ours in darkness and *much* worse than ours in daylight. People underestimate just how well we can see compared to most other animals.

See the graph on page 5 here:
https://www.researchgate.net/publication/296156154_Night_vision_in_barn_owls_visual_resolution_under_dark_adaptation