Maybe monochromatic is not the right word, what I mean is light consisting of a single wavelength (i.e. a spectral color) versus light composed of photons of multiple wavelengths (intermediate color).

For example, suppose we had a single, violet "laser" and a set of "lasers" combining into a purple color.*

Is it possible to combine the latter light sources such that their composite would perfectly match the violet one such that both look the same to a human eye (assuming perfect alignment)?

And would they look the same to all human eyes?

My guess is a no, because people might have different susceptibility to red and blue hues, and their aggregation functions may differ as well.

* Apparently, there are alternative definitions to distinguish the two colors (purple is reddish, violet bluish), but I am referring to the ones found in Wikipedia: Purple being an intermediate color and violet being a pure spectral color.

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    $\begingroup$ The short answer is no. Because of metamerism, the human vision system cannot distinguish monochromatic light from the infinitely many metameric equivalents that elicit an identical tristimulus response as that of the monochromic light. $\endgroup$ – tchrist Apr 23 '17 at 3:56
  • $\begingroup$ There might be nonlinearities in the photoreceptor, and chromatic aberrations of the lens (optics) that might allow a well trained eye to discriminate using tricks...(just a guess, hence not an answer) $\endgroup$ – Memming Apr 23 '17 at 12:27
  • $\begingroup$ Err... You're presumably reading this on a computer display, no? Which produces colors by combining essentially monochromatic red, green, and blue pixels. So can you see differences? $\endgroup$ – jamesqf Apr 23 '17 at 18:46
  • $\begingroup$ @jamesqf well, people can perceive flickering on computer displays, even on LCDs with temporal dithering, as I do, and there may be reasons why people distinguish between purple and violet, even leading to different names for the "same" perceived color. And if you look closely at an RGB display, you can see red, green and blue dots. Also, some people are tetrachromats and can see differences in skin tones where trichromats cannot. Some can even see polarization. Certain purple and violet hues might look the same to some people but different to other people, unless proven otherwise. $\endgroup$ – Archimedix Apr 23 '17 at 21:19
  • $\begingroup$ @jamesqf also, I don't have proper, comparable monochrome light sources to compare them in any scientifically significant manner, much less people to experiment on. $\endgroup$ – Archimedix Apr 23 '17 at 21:24

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