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This question already has an answer here:

I do not understand why human eye sees different colours from the LED TV/screen. Especially violet.

For example, how we get yellow color on TV. There are 3 small diodes Red, Green Blue in LED screen and when we see yellow, that means Red and green diodes are on and blue is off. This I understand, because wavelength for red approximately 600 nm, for green 500 nm and yellow in the middle, let say 550 nm. In this case 600 for red + 500 for green gives 550 in average, that is yellow. it is ok, good explanation.

But what about violet? Violet wavelength is 300 nm, We get it on TV if we combine red and blue. red is 600 nm, blue is 400 nm and in average I expect that we will see it as 500 nm green. But why we see it as violet which should be 300 nm? Anyway, we cannot get at all 300 nm if we combine red (600), green (500) and blue (400).

All wavelengths here are very approximate from the top of my head maybe +/- 50 nm or even more. Exact numbers do not matter, the main point is the idea how human eye see different colors.

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marked as duplicate by Bill N, Kyle Kanos, Jon Custer, sammy gerbil, JamalS Apr 12 '18 at 12:22

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ It's more a question of physiology than physics. Do you mean why do we perceive 128,0,255 RGB as the same as violet? $\endgroup$ – Martin Beckett Apr 10 '18 at 16:14
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    $\begingroup$ A good explanation of the topic jamie-wong.com/post/color $\endgroup$ – Martin Beckett Apr 10 '18 at 16:20
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The perseption of 'color' by humans is a quite complicated process and it can not reduced to calculate the mean wavelength of all colors from a given spectrum to get the 'right' percieved color.

Actually, the human eye has three different perceptors (for colors and one extra for grey) which are reacting mainly on red, green and blue light (simplified). So, when a source emmits any spectrum (like an LED screen, each of the three perceptors react with a certain intensity. The combination of theese three outputs (in simplification: Three numbers) create some sort of color impression in our brain.

Therefore, if you really want to make the calculation, you must calculate the reaction of each of the three perceptors on the weighted wavelenght send by the LED and the combination of these three results should give you the right answer.

If needed, I can try to find out more specific properties of the perceptors and show you numerical results, but maybe, catching the idea may be sufficient for your queation.

Otherwise, give me a note and I will figure it out more specific.

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  • $\begingroup$ Thanks for the clarification. If we talk very simplified, Do I correctly understand, that 2 light waves of red and blue colors mixed together (600 and 400 nm wavelength) give the same response in the eye perceptors (same brain color impression) as 1 violet light wave with 300 nm wavelength? If yes, it will answer my question completely. $\endgroup$ – Zlelik Apr 10 '18 at 21:15

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