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I know that if I look at an electromagnetic wave with a wavelength between 400 and 700 nm, I will see it as having some color. Is the converse true? I.e., can every color be generated by a single electromagnetic wave (with a given wavelength)? Take, for instance, the RGB space. Every color there is generated by means of three waves (one red, one green, one blue). Could each of these colors also be generated by a single wave?

As an example, consider the visible light spectrum illustrated in the following figure. Adding a wave with a wavelength of approx. 650nm (red) and one with a wavelength of approx. 470nm (blue), I get the color magenta. From the picture, it would seem that I could also get this color with a single wave with a wavelength of approx. 420nm. So, could I do this for every conceivable color?

enter image description here

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  • $\begingroup$ How about "white"? $\endgroup$ – BowlOfRed Apr 20 '18 at 16:25
  • $\begingroup$ Or how about brown? $\endgroup$ – Pieter Apr 20 '18 at 20:00
  • $\begingroup$ White is not a color, as I understand it. And what about brown? What's special about it? $\endgroup$ – LGenzelis Apr 20 '18 at 20:27
  • $\begingroup$ @LGenzelis Brown, among other colors, is composite. $\endgroup$ – Kyle Kanos Apr 20 '18 at 23:25
  • $\begingroup$ @KyleKanos but so is magenta, as in the example I gave in the post (after editing it). $\endgroup$ – LGenzelis Apr 21 '18 at 17:00
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So I think what you're asking is if a EM wave packet that includes multiple wavelengths can be perceived as the same as a single coherent EM wave. If that's the case, I think this problem has more to do with our biology and what our eyes see and our brains interpret than pure physics. From a purely physical perspective, a single coherent EM wave is qualitatively different than a wave packet that contains many different EM waves. One could always conduct physical experiments to distinguish between the two (e.g. run the wave through a spectrometer, or a diffraction grid). Whether our eyes can distinguish between the two I'm not certain since I'm a physicist, not a biologist.

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  • $\begingroup$ "So I think what you're asking is if a EM wave packet that includes multiple wavelengths can be perceived as the same as a single coherent EM wave". I edited my question, so as to make it more clear. $\endgroup$ – LGenzelis Apr 20 '18 at 20:38
  • $\begingroup$ I'm still getting the same interpretation of what your question is. Was there something else you wanted to know? "Every conceivable color" is also quite ill defined...I feel like your question is more of perception than physics. From a physics perspective, my answer doesn't change. A single coherent wave is qualitatively different than two waves combined in a wave packet. $\endgroup$ – enumaris Apr 20 '18 at 20:41
  • $\begingroup$ But I am not interested in every quality of the waves, just their color. It is as if I asked if I can get an amount of sand that weights the same as some amount of iron, and you answered that the question is not about physics because sand and iron are qualitatively different. $\endgroup$ – LGenzelis Apr 21 '18 at 16:54
  • $\begingroup$ But color is a perception issue isn't it? A biological perception of what color is. I addressed that in my answer as well...maybe I'm misunderstanding...but what do you mean by a purely physics definition of color? $\endgroup$ – enumaris Apr 21 '18 at 17:30
  • $\begingroup$ To be honest, I am not sure. I am not a physicist. I am just physics-curious. If this question can not be answered here, it's probably pointless to keep trying. I will save the question until I run into a neurologist (or maybe psychologist?) who has a background in physics. $\endgroup$ – LGenzelis Apr 22 '18 at 20:36

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