Do we see bands of color in a rainbow because of the physiology of eyes or the way the brain interprets the frequencies? or are those bands of separate colors a product of unequal refraction?
In: Physics
All color perception is a product of how your eyes respond to certain wavelengths of light. However, there is absolutely nothing different about how rainbows work, that makes this color perception different from any other situation in life. So I expect you don’t need or want an explanation for how color perception works, as that would be a bit condescending.
I suspect you’re asking about whether there is an actual, physical difference in the light itself coming from a rainbow. The answer there is yes. The light truly is different. There really is red, orange, yellow, etc. light and it really is coming from different locations in the sky into your eyes. It is not an optical illusion created from how that light interacts with your eyes or how those signals are interpreted by your brain. The red part is actually… y’know… red. At least as much as anything else in life is red.
The raindrops in the air are working like tiny prisms. When sunlight hits them, they are splitting the white light into a spread of rainbow colors, just like those famous pictures of Newton splitting a light beam shining through a slit with a triangle of glass. All of the drops of water in the air are doing this, all around you, at the same time, in all directions.
But it is only a certain set of drops, at a very specific place in the sky, that are splitting those colors in just the right direction to shine direction into your eyes. That position is always at an angle of 138 degrees away from the sun, or perhaps more simply, 42 degrees upwards from the point opposite the sun in the direction you’re facing.
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