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Eye resolution and colour

  1. Apr 14, 2007 #1
    hi, i was just wandering what colour you see best in a why?, i mean if a room was to be flooded in red blue or green what would be the best for the resolving power of the eye.

    thank you very much, alex
  2. jcsd
  3. Apr 14, 2007 #2
    Your eye isn't like a camera; it doesn't have a resolution. What do you mean by "best for the resolving power?"
  4. Apr 14, 2007 #3
    i think hes just asking which one we see with most clarity. I think it depends more on the contrast with the colors around it than the individual color
  5. Apr 14, 2007 #4
    If I remember correctly the eye has different number of each color of cones that allow it to percieve color. About 2/3 of the cones percieve the color red. About 1/3 are for green and the 3 or 4% that I rounded off are meant to see the color blue.

    I seem to remember reading some observations that all of the colors are perceived equally well in a normal eye. There was some speculation that some enhancement within the brain allowed blue to be seen as well as red. Whether the number of cones might have something to do with what color a person sees best, I have no idea.

    Here are a few neat links with some information that might be useful to you.
    Last edited: Apr 14, 2007
  6. Apr 14, 2007 #5
    The eye will react most sensitively to a certain yellow, corresponding to the wavelength that the sun outputs more then any others.

    You can see what I am talking about by playing with this applet, although it doesn't have the sun as an example, but the 5000k is close:

  7. Apr 14, 2007 #6


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    Because the sun produces most output at a given wavelength, why does it follow that the eye "will" react most at that wavelength?

    Filtering by the earth's atmosphere has a large effect. The radiation power spectrum in low light conditions (cloudy skies, dawn and dusk, moonlight) is very different from the sun's black body spectrum.

    The eye did not evolve for the purpose of looking at the sun. In fact humans have a strong reflex action to avoid looking directly at the sun, except when it is near the horizon and not very bright.
  8. Apr 14, 2007 #7


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    The peak sensitivities don't occur at true, blue, green, and red. Here's a link to an article that shows the colors for the peak sensitivities for each color.

  9. Apr 14, 2007 #8


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    I am pretty sure that the eye is most sensitive to green.
  10. Apr 15, 2007 #9
    The peak of sensitivity of the "normal" eye in normal illumination (not in low level illumination) is for 550 nm (bright green).
    Look for the CIE curve.

    The cones are not sensitive enough at low levels of light. In the dark only the rods are sensible enough. In low light you do not perceive colors. Rods are far more numerous than cones.
    See this site:

    Of course the eye, as a camera, has a resolution. It is given by the aperture of the iris and the focal length. It corresponds fairly well to the distance between rods in the retina. It is supposed to be one minute of arc. That is you are supposed to resolve one thirtieth of the diameter of the moon.
  11. Apr 15, 2007 #10


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    Presumably, the eye would evolve to be most sensitive to the wavelengths most prevalent in one's surroundings, which would presumably be the precisely those wavelengths the sun emits in greatest abundance.
  12. Apr 15, 2007 #11
    Most of the light emitted by the Sun is in the infrared. But only a few species are sensible to these wavelengths.
    One possible explanation is that eyes developed in water and in water there is not infrared. And we inherited the eyes of mollusks and fishes.
  13. Apr 15, 2007 #12


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    Yes, but the infrared is a much wider range of frequencies than the visible spectrum, so that's a really poor comparison. Assuming things scale proportionally, it would take about 40 different kinds of cones to see in the infrared to the same amount of precision as we can see in the visible spectrum.

    Put differently, if an organism could only see as much of infrared wavelengths as we can see in the visible wavelength, there would be much less light available to said organism.

    NASA's site gives another useful bit of information:

    The picture at the bottom suggests that, if I understand it properly, in addition to the blackbody effects we're discussing, that radio and visible light is essentially all of the sunlight that penetrates the atmosphere.
  14. Apr 15, 2007 #13
    Radiation coming from the Sun is almost identical to the radiation of a black body at the temperature of the Sun. The atmosphere filters more or less some bands, but is not very important. Unless of course if you want to use the absorbed light.
    Infrared spectrum is, as Hurkyl wrote far larger than the visible one. But the energy density per hertz (or per nm) if also bigger. If nature have decided that our visible band was the infrared, it would not have been forced to make us see all of what we name IR spectrum It could have decided that we should see say between 800 nm and 1600 nm. In this case just the almost same three different color captors would have sufficed.
    Anyway what is really important is the light and not the color. Color is just a complement. It helps to choose ripe fruits. But to escape to a predator it is the sensitivity in the night which is vital. Nature could have chosen another band of frequencies.
  15. Apr 16, 2007 #14


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    (When you presume you make a pres out of u and me.) There's plenty of data that shows otherwise.
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