You know how at twilight, blue lights seem to have a fuzzy halo (or a fuzzier halo than the other colors (you should get your eyes checked))?
TIL: ...why blue lights always look so blurry! It's a combination of chromatic aberration and our evolutionary attempt to control that aberration. Think of a prism, spreading white light into a rainbow. It does this because light of different colors is deflected differently as it transitions between two substances (with different refractive indexes).
The human eye has two kinds of light receptors, rods and cones. Rods are responsible for seeing in the dark and providing peripheral vision. They only detect one wavelength so we can only see in black in white in very dark environments. The nice thing about rods is that they are found all over the retina, so you have a full wide-angle view.
Cones, on the other hand, only work well in brighter light and come in 3* flavors: red, green and blue. The problem with this is chromatic aberration. The image coming into your eye is bent by the cornea, lens, and various fluids. The three wavelengths separate from each other and project three slightly offset images on the retina. You can see absorbance curves for rods and cones above. Can you tell which one is the odd color out? Blue! When your eye focuses light on the retina, it does the best it can to minimize the aberration, so it focuses somewhere between the focal points of the red and green cones and just ignores blue.
So why don't you see blurry blue things all the time? To attempt to counteract its shoddy focussing, the retina messes with the distribution of the different color detecting cones. Whereas rods are all over the place, cones are almost entirely in the center of the eye, called the fovea. But blue cones are both less prevalent throughout the retina and not present at all in the center of the fovea. Your brain does some photoshop magic to make sure you think blue things are blue even though you don't directly see blue in the center of your vision.
So when lighting is dim and cones are strained, blue gets the shortest end of the stick. And that is why blue lights look fuzzier than other colored lights.
*There is actually a fourth human cone that can detect yellow wavelengths. It's absolutely fascinating but frustrating to talk about because we don't have words to describe what these people see. There's a great Radiolab podcast on it. Also, human eyes have nothing on the mantis shrimp.
So why don't you see blurry blue things all the time? To attempt to counteract its shoddy focussing, the retina messes with the distribution of the different color detecting cones. Whereas rods are all over the place, cones are almost entirely in the center of the eye, called the fovea. But blue cones are both less prevalent throughout the retina and not present at all in the center of the fovea. Your brain does some photoshop magic to make sure you think blue things are blue even though you don't directly see blue in the center of your vision.So when lighting is dim and cones are strained, blue gets the shortest end of the stick. And that is why blue lights look fuzzier than other colored lights.
*There is actually a fourth human cone that can detect yellow wavelengths. It's absolutely fascinating but frustrating to talk about because we don't have words to describe what these people see. There's a great Radiolab podcast on it. Also, human eyes have nothing on the mantis shrimp.
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