Eli5 How is frequency related to perceived color?

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What’s the mechanism behind translating a wave frequency to a color for a human?

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Anonymous 0 Comments

Your color sensing cells in your eyes come in 3 types. Each is sensitive over a range of wavelengths to different degrees, peaking in sensitivity at a certain wavelength and falling off to the sides.

https://upload.wikimedia.org/wikipedia/commons/thumb/1/1e/Cones_SMJ2_E.svg/287px-Cones_SMJ2_E.svg.png

So any specific wavelength of light ends up activating one or multiple color cells in a region to different degrees that our brain merges together and interprets as a single color. It doesn’t react to a single photon either, rather a number of photons which may even be different wavelengths over a short period of time.

Which is also why we can see non spectrum colors like magenta. The color is a result of the specific combination of activation of different color cells so receiving red and blue wavelengths in the same area reads as magenta. Similarly receiving multiple colors of the actual spectrum that are nearby can mix to a color that duplicates the response to a single wavelength. A violet and cyan can mix to blue.

Receiving an even range mixes to white when interpreted.

As another note that peaking and overlap of color cells is why we have trouble telling certain wavelengths of light apart. Or to rephrase why the light spectrum from a prism seems to separate in distinct color bands.

Anonymous 0 Comments

There are 3 different proteins in your eye called ‘photopsins’ which hold each hold much smaller molecule, retinal, in slightly different shapes. These proteins are present in the 3 different kinds of colour-perceiving cells, cone cells.

Due to some funky physics, different wavelengths (colours) of light will be absorbed more or less by a retinal molecule depending on how it is being held by the photopsin protein. When the retinal is hit with light that it absorbs well, it changes shape, leading to a change in the shape of the photopsin protein. The cell quickly recognises this and sends a signal down the line to say that some red light was absorbed, for example.

There’s a great video by Steve Mould if you’d like to know a little more in depth: https://www.youtube.com/watch?v=dvovtbLGaUw&ab_channel=SteveMould

Anonymous 0 Comments

Adding to the other answers: when your cones perceive wavelengths they don’t just make your neurons associated with that color fire… They fire faster or slower depending on how close the wavelength is to the ideal wavelength that cone is associated with.

Your cones ideal wavelengths are roughly red, green, and blue.

So, if you see purple you might get red firing at 100, blue firing at 90, and green firing at 10 and your brain perceives that as purple.

Of courses your cones are a mechanical biological process that has some flaws. For example, if your cones get too “tired” they will stop firing. That means you can fool your cones into tiring out then looking at a color and see something completely different.

There are also color combos your eyes can’t see because the cones pick up more than just their ideal colors so there’s no way to shut up certain cones in order to get the signal for specific colors. Wild huh?

Anonymous 0 Comments

Take the photoreceptor details from the other answers; here’s how the light frequency actually fits in:

Light can only interact with atoms if it contains EXACTLY the right amount of energy to move an electron one of its allowed distances. And the frequency of the light is ALSO the energy content of the photon. They’re the same concept just on different scales. So if light is the wrong frequency for a given set of aroms, it just passes on through and doesn’t interact.

So… a given configuration of atoms will only interact with certain frequencies of light, based on wha the elections are up to. Which is a fancy way of saying that certain stuff is a certain color. But it also means that by having a given configuration of atoms in specific proteins in specific cells (the photoreceptors from everyone else’s answers), those cells interact with the desired frequency (energy) of light, allowing you to see that light.

Anonymous 0 Comments

Hi. Doctor here.

Frequency and wavelength of light are a measure of the energy of that light. Since color does not exist in reality, and is an invention of the brain to make sense of the different wavelengths of light the retina detects, the color receptors in the retina fire at different rates under different wavelengths. Those combinations of firing rates of all 3 receptor types is processed in the brain to produce what we perceive as color.

For example, let’s say a light with wavelength of 650nm makes the color receptors fire like this:
Red: 98-100%
Blue:0-1%
Green: 0-1%

This 100-0-0 combination in brain means Red. So we perceive the color red.

Hope this helps. 🙂