I understand that a pupil getting smaller lets less light in so in bright settings it reduces the total amount of light hitting the eye but why? Wouldn’t the intensity of light be the same? How does this not effect peripheral vision if the hole that we see from gets smaller?
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There’s no such thing as “intensity” of light, at least for our eyes. Light has a wavelength, which roughly translates to color, but that’s not what pupil dilation affects. Pupil dilation physically prevents some amount of light from entering the eye by closing the aperture. Less light entering the eye means less stimulation for the light receptor cells, which makes your brain feel like it it less bright and helps you see better contrast.
Your eyeball is a flexible lens. It can change its shape to affect how the light moves through it, basically “bending” the path that light follows. That includes light from the periphery of your vision, so your eye can compensate for the dilation, to a degree. But peripheral vision is also simply less detailed and less critical than your central vision, so a loss of peripheral vision is an acceptable price to pay to maintain clear, sharp central vision at various light levels.
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