You see colour using three different kinds of cones in our eyes, and these cones can be either red, blue, or green. So where does yellow come in? Green consists of yellow and blue – but how would you only see yellow and not the blue that would make it green?
In: Biology
* Each set of the cone cells respond to a range of wavelength.
* Some of those ranges overlap.
* Yellow objects reflect light wavelength at a frequency that triggers both the red and green cells to a certain degree.
* Your brain interpret that response as yellow.
That’s also the way monitors trick you into thinking that the pixel is yellow. The red and green lights are calibrated to give you the same response of cone cells to make your brain interpret that as yellow.
You are right that there are three types of cones, L, M and S. And these are centered around different wavelengths and therefore different colors. But it is not red blue and green. This is what we use to make artificial colors. It is more purple, green and yellow. But each type of cone detect colors in a wide band and there is even lots of overlap. So even though the M cones are centered around green they still register about 70% of the yellow light. Your brain just translates that when there is more signal from the L cones then the M cones the light is yellow and when there is more signal from the M cones then the L cones the light is green. When there is only signal from the L cones the light is red because the M cones can not see much red at all. This is why we use red LED lights when making artificial light as we can trigger only the L cones. So what we can do to make it appear yellow is to combine a green and red light which will fool your brain into thinking there is a yellow light.
The colours are just your brain interpreting the electrical signals received by the eyes.
They aren‘t ‚real‘ per se.
They could just as well be numbers.
And numbers make it easier to see how the colour yellow ‚appears‘ in the brain,
So if light activates both green and red receptors, it would create the average ‚number‘ between the two.
So even if green could only send 1 and red only send 9, the brain making the average would get a 5.
Without any of the receptors in the eye ever sending a 5 themselves.
Same with the colour yellow. That’s just what the brain chooses to make things appear that activate both the red and green cones
The cells in your eye have fairly broad sensitivity ranges.
You don’t have a cell dedicated to “yellow” at 580nm but you do have the M and L type cone cells that can both detect this range.
Incoming yellow light triggers both cells at a certain ratio, and your brain interprets this as “yellow.”
This is also why TVs and printers can fake yellow without actual yellow die/light – they just have to trigger the two cones in the same ratio.
Green consisting of yellow and blue is only true in the context of mixing pigments and doesn’t apply here. The cones of eyes measure (in extremely simplified terms) how close is the wavelength of light to some specific color – green, red, blue. The closer to this ‘baseline’ color of the given cone type the light is, the more it is stimulated. The wavelength of yellow is between red and green, and thus it stimulates both types of cones. This signal is what your brain interprets as yellow. You can, however, also get the exact same stimulus by mixing green and red light, which is why RGB monitors can give you more than three colors.
You’re thinking of mixing paint where yellow+blue=green. With light color mixing works differently – it’s red+green=yellow. If you add blue to that (red+green+blue) you actually get white.
Because your eyes are based on seeing light they see the red green blue light mixing.
If you open a paint program on your computer you can experiment with how red green and blue light mixes using the color picker, because monitors also work by red green blue light.
There are two sets of primary colors: Additive and subtractive. Additive primary colors are Red, Green and Blue. Most people learn about Subtractive Primary Colors as Red, Yellow and Blue, but more accurately its Cyan, Magenta and Yellow. We’ll come back to this in a bit.
Additive Primary Colors apply when you are combining different colors of light. Pretend you have three spotlights, all aimed at the same spot. One of them is red, another green, and the third one is blue. If you turn on the red light, the spot lights up red. If you add in green light, the spot lights up yellow. And if you add in the blue light, the spot is now white. If you take away the red light, leaving the green and blue, the spot is now a bright turquoise color, called cyan. This is the way you can create pretty much any visible color using three separate lights. Televisions and other video screens exploit this effect by having three different colored lights for every pixel – they’re very small and very close together, but if you look at your screen under a microscope, you’ll see them. And by turning each light on at different brightnesses, you can create millions of individual colors.
Subtractive primary colors are used when combining different colors of pigment – that’s a fancy word for paint. If you combine red and blue paint, you’ll get the color purple. Yellow and blue, you get green. Red and yellow – orange. However, in professional printmaking, the primary subtractive colors they use are actually Cyan, Magenta, Yellow, and Black. This allows for the creation of the same range of colors as you can with light, but instead you’re mixing paint.
There’s some argument to the idea that we never actually “see” yellow, because we only have cones for red and green – instead our brains just combine the two activated sets of cones and fills in the details. I can’t speak much to this because I don’t understand the physiology of the eye nor the cognitive processes that augment it.
It works like the pixels in a monitor. Light colors are ‘additive’, meaning that to get white you mix all three primary colors together in equal and full intensity, and to get black you turn them all off. So to get secondary, tertiary, etc colors you would turn down the primary color that you don’t want to see.
In the visible spectrum of light, yellow is bookended by green and red. So to get yellow you mix the two colors that overlap with yellow (green and red), but not the color that doesn’t overlap with yellow (blue).
The cones is our eyes are not tuned to just one wavelength but they just peek there. They get a bit of a response from wavelength above and below that.
The entire viable spectrum is covered.
Our brain figures out the rest.
If an S cone recognizes a bright light but M and L looking in the same reaction don’t, than our brain decides that light must be blue.
If all three type of cones see something with equal intensity it mus be white.
L and M cones have a huge overlap. It is only light that is very red that gets an reaction out of L cones but not M cones.
If both L and M cones react ( but not the S cone) than the color must be somewhere where the cones overlap, depending on the response that might be yellow.
Basically the brain compares the response of the cones and assigns that to a “color” that is we perceive as one in the middle of spectrum between the reaction from the cones.
Things get weird when we have s and L cones react but not M cones. The m cones are between the S and L ones spectrum wise. There is no single wavelength of light that would result in that reaction, our brain simply can make up colors that don’t correspond to wavelength of light, like purple.
The colors we see with out brains are just ratios of the reaction of the different cones in our eyes that only partially correspond with the actual physical reality of wavelengths of light, that we ‘see’
The real question you should be asking is “how the hell do we see purple”, since there is no purple in the visible light specturm
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