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MIxed and reflected color frequencies.

  1. Sep 10, 2011 #1


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    When I shine two different lights at a single spot on a white screen, say, yellow and blue, they both hit the spot and get reflected all mixed up and I see green. Thats all fine, but what is the actual structure of that reflected, in this case, green light? Is it a ordinary green photon with its corresponding frequency? (say, 510nm )or is it the same blue and yellow photons, but our eyes just detect both at the same time, from the same spot, and interpret it as green?
  2. jcsd
  3. Sep 10, 2011 #2

    We would not perceive green light in combination of blue and yellow light though I do not know what color we perceive of it.

    Instead, three fundamental color of paint are Cyan, Magenta and Yellow. Cyan absorbs Red light. Yellow absorbs Blue light. So mixed paint of Cyan and Yellow absorbs Red and Blue lights, thus Green light, which consists three fundamental light color with Blue and Red, mainly remains in the reflected light. It consists actually of green photon.

    Last edited: Sep 10, 2011
  4. Sep 10, 2011 #3
    The light reflected from the white screen contains the yellow and blue photons.
    The normal reflection does not change the frequency of the photons.
    The sensation of green is a physiologic effect due to simultaneous excitation of the receptors in the retina. The reflection is irrelevant actually. If you send the two beams directly to the eye you'll see green too.

    The mechanism of the color vision was disused extensively in a thread some time ago.
  5. Sep 12, 2011 #4


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    So, with nothing but my natural sensors (eyes), I cannot know if I am looking at a green color (or any other color) or a combination of two or several..
  6. Sep 12, 2011 #5
    if we paint rainbow's color on a circle top and rotate it,wecan see color white. that means our eyes have a time limit to distinguish different colors.
  7. Sep 13, 2011 #6
    Yes, this effect is called http://en.wikipedia.org/wiki/Metamerism_(color)" [Broken]
    Last edited by a moderator: May 5, 2017
  8. Sep 13, 2011 #7

    Is it true we see green color when blue photons and yellow photons are coming together into eye ?
    As for paint mix of blue paint and yellow paint cause deletion of two complimentary colors and only almost green color can be reflected.
    how about addition of blue photon and yellow photon?

    Mix of various paint is black, however, mix of various photon is white.

    Last edited: Sep 13, 2011
  9. Sep 13, 2011 #8
    Blue paint reflects more blue photons and yellow paint reflects more yellow photons. A mixture of blue and yellow paint will reflect both blue and yellow light (unless there is some interaction between the pigments which will change their nature). For solid pigments (like oxides) you can still see individual grains (and their individual color) with a microscope whereas the overall sensation is that of the "mixture color". The yellow pigment does not "eliminate" the blue photons reflected by the blue pigment.

    You can think it in terms of "eliminating the complementary color" but this is just an useful tool. The result is the same but the physics is not.

    There is no "addition" of photons. Mixing beams of photons with various frequencies does not change the nature of the photons (in the usual conditions discussed here).

    And yes, seeing some colors (physiologic response) can be due to excitation of retina by more than one combination of photons.
  10. Sep 13, 2011 #9
    This is actually a good thing. It means our color printers do not need ink cartridges with 10 million different colored inks inside. Just three will do.
    Last edited by a moderator: May 5, 2017
  11. Sep 13, 2011 #10
    See figures on additive and subtractive color mixing in Wiki Primary color. http://en.wikipedia.org/wiki/Primary color [Broken]
    Last edited by a moderator: May 5, 2017
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