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I have read this question:

Explanation about black color, and hence color

where John Rennie says:

For example suppose you're looking at red light. Only the "red" cones will generate a signal and your brain interprets this as red.

https://pages.jh.edu/~rschlei1/Photographic/violet/violet.html

Red light more strongly stimulates the red-sensitive cone cells than the green-sensitive cone cells, and the brain processes this ratio as a shade of red.

enter image description here

Now there is some contradiction, because our perception is in our brain, but our receptors in our eyes are developed for trichromatic vision and based on this diagram, more then one type of cone will be activated if any kind of light (monochromatic or not) shines on our eyes. The diagram is not fully accurate I believe, because it does not show for example how sensitive the Short cones are in the longer wavelength range or how sensitive the Long and Mid cones are in the short wavelength range, but based on the statement in the article, all cones should be somewhat sensitive all along the visible range.

The question is, whether if monochromatic light shines into our eyes, will that activate multiple types of cones or only one type of cone?

Question:

  1. If monochromatic light shines into our eyes, will that activate multiple types of cones or only one type of cone?
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    $\begingroup$ Judging by the diagram, it will activate multiple cones... however to a different level - hence our ability to distinguish colors. $\endgroup$
    – Roger V.
    Jun 3, 2020 at 16:32
  • $\begingroup$ Another important aspect is that cones are distributed inhomogeneously: our peripherial vision is less sensitive to color and more sensitive to movement. $\endgroup$
    – Roger V.
    Jun 3, 2020 at 16:37
  • $\begingroup$ There's actually a lot of interesting research about color perception & physiology. See this page and these posts. $\endgroup$ Jun 4, 2020 at 23:35

1 Answer 1

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If monochromatic light shines into our eyes, will that activate multiple types of cones or only one type of cone?

Let's take for example monochromatic light with wavelength 520 nm (i.e. a yellow wavelength).

Then your diagram (with the spectral sensitivity of the 3 types of cones) answers this question easily.

enter image description here

  • L-type cones respond with strength 0.68
  • M-type cones respond with strength 0.88
  • S-type cones respond with strength 0.02

So yes, all 3 types of cones are activated, but for this wavelength the S-type cones are activated only very little.

From the ratios between these 3 numbers the brain concludes: It is yellow.

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    $\begingroup$ Note that these spectral sensitivities are normalized to fractions of maximum. The absolute sensitivities at their maxima are different. $\endgroup$
    – Ruslan
    Jun 3, 2020 at 17:22
  • $\begingroup$ Thank you so much! $\endgroup$ Jun 3, 2020 at 21:18

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