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How can there be purple?

  1. Mar 15, 2009 #1
    How is there a color "wheel"? Color is just visible light on the EM spectrum which has red at one end and purple at the other end. But on the color wheel purple and red come back around and touch. How is that possible?

    Purple just doesn't seem to make sense to me. Purple is blue and red light mixed (magenta might be the more accurate term), or if you just take the middle of the visible light spectrum (green) out of white. So, for blue to become violet, it'd have to start heading toward "red" again, which is on the other side of the visible light spectrum. How does it go toward red again? It just doesn't make sense to me.

    I'm really racking my brain out here. lol
  2. jcsd
  3. Mar 15, 2009 #2


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    Staff: Mentor

    How color is produced in nature and how it is perceived in the eye are two completely different and unrelated things. The color wheel is a representation of how your eyes generate colors, not how nature generates colors.

    Strictly speakiing, light generated in nature doesn't have "color", it is just different wavelengths. Different animals percieve "color" differently because their eyes are adapted to process different wavelengths.

    Also of note: purple and violet aren't quite the same thing - violet is a "spectral" color (it is part of the spectrum) whereas purple is generated by mixing. Here's the wiki on the subject: http://en.wikipedia.org/wiki/Violet_(color [Broken])
    Last edited by a moderator: May 4, 2017
  4. Mar 15, 2009 #3


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    Ergo, when you're seeing purple, you're seeing more than one spectral colour. Or more accurately, you're getting both your red and blue receptors stimulated.
  5. Mar 16, 2009 #4
    Thank you so much! You guys are awesome!

    I wonder why our eyes opted to simulate violet with red and blue.
  6. Mar 16, 2009 #5


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    You've got the question backwards. The question is:

    I wonder why our eyes opted to show red and blue as violet.
  7. Mar 16, 2009 #6
    Hmmm, now I'm confused. I thought we couldn't see violet so our eyes show it as red and blue?

    "Spectral violet is outside the gamut of typical RGB color spaces, and although it can be approximated by that color shown below as electric violet, it cannot be reproduced exactly on a computer screen."

    "Violet is a spectral color (approximately 380-420 nm), of a shorter wavelength than blue, while purple is a combination of red and blue or violet light.[7] The purples are colors that are not spectral colors – purples are extra-spectral colors. In fact, purple was not present on Newton's color wheel (which went directly from violet to red), though it is on modern ones, between red and violet. There is no such thing as the "wavelength of purple light"; it only exists as a combination.[3]"
  8. Mar 16, 2009 #7


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    Violet light excites the blue receptors. Actually, http://en.wikipedia.org/wiki/Trichromatic_vision" [Broken]; it just excites the blue receptors the most.

    Perhaps this is why we register violet as distinct from blue - our brain can tell the difference between
    80%blue, 10%red (which might read as blue)
    80%blue, 5%red (which might read as violet.)
    Last edited by a moderator: May 4, 2017
  9. Mar 16, 2009 #8
    So violet is just an extreme blue? I though violet was more "purple" looking than blue so wouldn't it excite the red receptors more than blue would?
  10. Mar 16, 2009 #9
    True violet has always been, as far as I can recall, the extreme blue end of the spectrum. When violet, or blue is mixed with red, then purple is obtained.

    That's how I've understood it. Violet stimulates the blue receptors in our eyes. Purple stimulates both the red and blue receptors.

    Unfortunately, many have interchanged the two as if they were synonymous, which they are not.

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