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Visible spectrum

  1. Aug 25, 2004 #1
    ... is the visible spectrum of light supposed to contain all the colors that we are able to see?
    if so, where is brown?
  2. jcsd
  3. Aug 25, 2004 #2
    Brown is a mix of color.
  4. Aug 25, 2004 #3
    We humans can only see what we see. As far as we know our human eyes only detect wavelengths between 380 nm and 650 nm or something close to that. We perceive light as continuous bands, but it is quantum level based. There may be some wavelength of light that our human eyes do not really perceive because the chemistry in the eye is not able to react to those wavelengths. So, for all intents and purposes, we see all that is available in the visible range, but there is the chance that we are missing some.
  5. Aug 25, 2004 #4
    the visible range is from 400nm to 750nm. And we are missing a lot. The range in wavelength of light is enourmous. The visible spectrum is soo small on the scale. We dont get to see microwaves, radio waves, x-rays, gamma rays. Imagine what the world would look like if we could getect all of these. :biggrin:
  6. Aug 26, 2004 #5
    Yea, the visible part of the spectrum has the least range out of all of them.
  7. Aug 26, 2004 #6


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    The VISIBLE SPECTRUM is defined as the light to which our eyes are sensitive. So by definition we can see all of the VISIBLE SPECTRUM. The entire EM spectrum is huge, the Visible spectrum is a insignificantly small band.
  8. Aug 27, 2004 #7
    ...What WOULD the world look like if we could see down to 200 nm and upto 900 nm? Or more!

    Could some one ...photoshop an image of what it would roughly look like. I'm guessing no.
  9. Aug 27, 2004 #8
    Well what colours would you assign to the low and high wavelengths? You can't just create a totally new colour.
  10. Aug 27, 2004 #9


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    Humans basically have three color receptors, each of which is based on a dye which absorbs different frequencies of light.

    It would be possible to imagine a being with three receptors "tuned differently" to cover a wider bandwidth. The details of what would be seen would depend on the new tuning of the receptors. A reasonable mapping could be done from what such a being would see into human color-space, if one definied the specific behavior of the beings receptors (there are many possibilities).

    If the hypothetical had more than three receptors, any analogy would fail. Their color space would have a different number of dimensions than ours.

    The visual percepton of color in humans is usually portrayed by a "chromaticity diagram", such as that shown at

    The main feature of the diagram is that any two colors on it add - if you select 2 points on the diagram, a color made by mixing them together lies on the line joining the two points.

    The diagram supresses one dimension (intensity) from the full 3-d color space.

    Note that the fully saturated colors (monochromatic light, like the colors in the rainbow) are on the outside of the diagram, while white light is on the inside, near the center.
  11. Aug 27, 2004 #10


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    Humans' perception of colour relies upon the three types of cones (or is it rods?), which have peak sensitivity in blue, green, and red bands respectively. In principle, you could wire up the nerves at the end of the rods to devices which detected any selection of three regions of the EM that you choose - you would then perceive the field of view of those devices in terms of BGR. You can achieve similar effects by using photoshop, converting (say) X-ray region1 to 'red', UV region2 to 'green', and radio region3 to 'blue'; indeed, many of the astronomical images you see (from, say, the HST, Chandra, XMM-Newton, Spitzer, even radio telescopes) use this principle.

    Different question: can your mind 'perceive' 'new colours' (other than combinations of BGR)? A: some lucky (or not) individuals actually posses this ability :surprise:

    1) synesthesics, whose brain wiring is 'interesting'; they can feel colours, and see smells (for example)
    2) some women (but no men): there are actually two types of red cones, each with slightly different wavelength sensitivity; the genes for cones are on the X chromosome, so a woman with one type of red cone gene on one X and the other on the other X can have retinas with each type sprinkled randomly (I've also read that there may be two green cones as well). A woman with this rich retina will 'see' colour more richly than a man (or woman without); unfortunately, she will have no way to convey to the unfortunate just what that richer sensation is actually like :eek:
    Last edited: Aug 28, 2004
  12. Aug 27, 2004 #11


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    I have often imagined that we could "see" RF frequencys, so every radio transmitter would be glowing a different color.
  13. Aug 27, 2004 #12
    Brown is a mixture of Orange and Green.

    Cones are for color (Red Cone, Green Cone, & Blue Cone) and Rods are for Black & White. There are more Rods than there are Cones for each color. That's why we see the stars at night in black and white. If we had enough cones, we could tell what color the stars are.
    Last edited: Aug 27, 2004
  14. Aug 28, 2004 #13
    Snakes in the pit viper family have small holes in their heads that sense IR radiation and likely assemble the image to look much like images they can see with their eyes. Other animals have similar senses that allow them to "see" more of the EM spectrum than we do.
  15. Aug 28, 2004 #14
    A color in the spectrum is specified by the wavelength, and so this is a one-dimensional quantity.

    The space of all possible colors would allow us to specify an intensity for each spectral color and so would be infinite dimensional.

    The colors we see are determined by the three different receptor types in our eyes and so this is a 3 -dimensional space. This can be specified as RGB or as hue (i.e. the pure, spectral color), saturation and luminosity (bring up a color dialog box on your computer to see this). Brown is then a dark orange-red color.
    Last edited: Aug 28, 2004
  16. Aug 28, 2004 #15
    The stoners favorite kitchen appliance would be the microwave as opposed the fridge.
  17. Aug 29, 2004 #16
    I think if we saw IR as red, and UV as blue, we would start to confuse IR/UV stuff with red/blue stuff.

    Whoa, nice lamb there mate, UV.

    "No... it's blue."

    If you edited your eyes somehow, (surgery, genes, whatever) up to 900 nm or above, could you see in the dark via thermal vision?

    *grabs a patent and rings up the military*
    Last edited: Aug 29, 2004
  18. Aug 29, 2004 #17
    Thermal imaging has been around for some time now. The police used to use it in helicopters to look into peoples houses. The supreme court ruled a few years ago that they need a warrant to image a private residence. Their reasoning was that behind closed doors a person has their right to privacy, and looking through their walls at them when they think they are unobservable is a violation of that privacy. Anything you do in front of an open window or door however is not protected by the right to privacy as people can naturally "see" what you are doing.
  19. Aug 29, 2004 #18


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    If the big bad wolf could see radio waves it would explain why little red riding hood said 'what big eyes you have, grandma'. I vote for yellow plus violet = brown. I could only afford the 12 crayon box when I started school.
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