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The physics of colors

  1. Oct 10, 2005 #1
    I hate to be 'that guy' who asks silly questions among a group of highly intellectual individuals, but I didn't know where else to go for a scientific answer.

    I'll provide the main question up front so you don't need to go digging for it: do colors exist outside the field of human vision?

    I've been having a conversation with my friend (an art major) about this, and I'm having a difficult time discovering the answer. I understand that the human eye has three cones (color) and three rods (amount of light) There are many animals out there that have more resources at their disposal. Most notably, the Mantis Shrimp, which has 12 cones capable of receiving color.

    I understand there is a difference between light and color - but I also [vaguely] remember that color also can be mapped out via a spectrum of wavelengths.

    I'm stumped, any insight?
  2. jcsd
  3. Oct 10, 2005 #2
    I can't answer all your questions because I suck but I can try.

    All the different colours that you see are a part of white light. I'm sure you know that when light refracts in a prism disperssion occurs, and you see the different colours that come out. When you see the red colour of a ball it is because white light has struck the ball, energized the electrons in the ball, the electrons jumped energy levels. Upon falling back to a lower level it releases photons of a certain wavelength which in this case is red's wavelength.

    I think the other colours that might exist belong to every other form of radiation on the electromagnetic spectrum besides white light which we can see. There could be a biological creature out in the universe on the planet koobahbahyumym with an eye designed so differently than that of humans that it can see x-rays or radio waves or I don't know...

    Anyways wait for someone who really knows what they are talking about to answer your questions. I might have written wrong things.
  4. Oct 11, 2005 #3


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    You might want to read a bit about the CIE chromaticity diagrams.


    The wikipedia article is probably the best place to start.

    These diagrams summarize the result of experiments on human vision. Three numbers describe any color, because the human eye has three color receptors.

    Note that this is possible because of the limitations of human vision. A full description of the actual spectrum of light requires a complete graph, with a plot of intensity vs wavelength. This would require, in principle, an infinite number of points. Human color vision is based on a very rough "averaging" of the spectrum, and because the human eye has 3 color receptors, it is logical to interpret this as a 3-d color space.

    This 3-d color space breaks down into an brightness value, which is a scalar, and a 2-dimensional "chromaticity" value.

    The CIE chromaticity diagram maps out this 2-d color space.

    Various different color-spaces can be defined in principle. The CIE is designed such that mixing together of any two colors generates a color that is on a straight line in the 2-d color space connecting the two colors - i.e. it is linear.

    This mixing together is done by mixing the lights (as on a CRT) - not by mixing the pigments (which is a different problem, because pigments subtract colors, rather than add them).

    The coordinate coordinate space has to be mapped out by experiment, but it turns out to have a horseshoe shape, with the fullly saturated colors lying on the outside of the horshoe, and white lying in the center.

    The aparatus used to perform these experiments consists of a white light source, a prisim (to separate the white light out into the fully saturated rainbow colors), a way to select three of these rainbow colors and control their intensity.

    See the above web link for more detail, or read more about "chromaticity diagrams" with a web search.
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