Shouldn’t common sense dictate that either both be one, or both be the other?
In: 1934
Purple isn’t on the electromagnetic spectrum, you’re thinking of violet. Purple is what we see when long and short wavelength light (i.e., red and blue light) hits our eyes at the same time. This stimulates our retinas in a way that no single wavelength does, so our brains produce a new color, called magenta. And purple is just a bluer hue of magenta, which makes it appear similar to violet, even though there is no violet light involved.
So there’s two different “purple like” colours or what some might consider purple or a mix of red and blues
True violet and magenta
True violet has a specific wavelength of light , easy for computers to properly display and something easy to explain as just a specific wavelength of light. It’s something that exists in a sense that we can say X nm of light is violet. Our eyes can see that wavelength and it fires off our cone receptors in a specific way that our brain says violet
Magenta however , doesn’t actually have exist , there is no magenta wavelength but we can still see magenta. This is because the way our cone cells in our eyes work is a trinary system , you sometimes have 4 rare and they generally are red blue green yellow with yellow being the rarity in a small lucky portion of people
When light comes in that is red orange , it sets off our red cones heavily and our green cones very little (depending on how orange is compared to red). Our brain takes the relative level from both and averages and says “that’s orange” , more green cone firing off and you get closer to yellow and then proper green.
When you get red and violet light coming it sets off both are red and blue cones which if our brain just averaged them would give us something closer to yellow/green then magenta. But our brain knows that green is a thing and the green isn’t being set off , so our brain makes up a colour since it should average to be green but it can’t be green so it makes up magenta
Paint does not give off light. It absorbs some of the light and the rest is reflected back. Interestingly, then, a strawberry ISN’T red. It’s every other colour EXCEPT red. It absorbs all the light except red, which bounces off, so that’s the colour we see. But it gives off no colour at all of its own. It only reflects some of the light that hits it.
So, when light hits purple paint (or anything else purple for that matter) the “stuff” in the paint absorbs all the light wavelengths of all the colours except the colours that make purple. It doesn’t matter where those colours are in terms of wavelength on the electromagnetic spectrum. They’re just the ones that bounce off and into your eyes.
Others have answered your question, but I’d just like to add that common sense doesn’t dictate, it only assumes.
I think there are two ways to percieve purple:
A:
1. Genuinely “purple” light enters your eyes. (Light with wavelength ~400nm)
2. This triggers both the parts of your eye that detect red, and those that detect blue.
3. You perceive this as purple.
B:
1. A mix of red and blue light enters your eyes. (Red at ~700nm and blue at ~470nm)
2. This triggers both the parts of your eye that detect red, and those that detect blue. [Exactly like scenario A]
3. You perceive this as purple. [Exactly like scenario A
You cannot tell scenarios A & B apart. Your eyes and b rain are not a perfect spectrometer that gives you objective information about the light that hits your eyes.
They are instead an approximated filter that gives a useful (but incomplete) subjective idea of the light around you.
One of the not-quite-true bits of information is that scenario A and B are the same.
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Similar things can happen for other colours, but in those cases, your eyes are less-wrong, because you’re basically detecting the average wavelength of the two mixed together.
Like wavelength wise, Red & Green combined feel like Yellow, and Yellow has a wavelnegth half-way between Red & Green. So perceiving the mix as the average isn’t quite *correct*, but it is still a good approximation.
It doesn’t really matter that we’re more-wrong about this with purple, but the idea that the colour wheel ‘loops around’ at purple is an illusion due to how our eyes and brains are wired.
I know it’s not the question asked, but I generally accepted pigment color and light don’t act the same considering if you mix all paint colors you get brown while the colors of the light spectrum combine into white light.
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