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What exactly are colours ?

  1. Jun 17, 2011 #1
    Hey guys. I have been thinking about it for quite a time but have not yet understood what exactly colours are. Are they in any way related to energy ? If so, how ?
  2. jcsd
  3. Jun 17, 2011 #2
    our eyes perceive radiation of wavelengths between 400 and 700 nanometers as colors due to an interaction with our eyes anatomy with our nervous system

    there are rods and cones at the back of our eyes. cones interpret photons as color.

    blue is higher energy than red because it has a faster frequency, hence a smaller wavelength.
  4. Jun 17, 2011 #3
    So, that must mean that different animals will see different colours. Even some humans would be seeing very slight difference in colours as the interaction between the eyes anatomy and nervous system would be slight different than others. Just slight.
  5. Jun 17, 2011 #4


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    Except for people who have selective color blindness, yes.

    Kinda mind blowing that colors are inventions of our brains, though, huh?
  6. Jun 17, 2011 #5
    Yes, colors are the names we give to the sensations we feel when the visual cortex is excited by nerve impulses coming from the retina when it's struck by light between 400 and 700 nm.

    The best quote I remember was on mySpace physics: 'My favorite color is 650 nm.'
  7. Jun 17, 2011 #6


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    Another interesting point is that some reptiles can see infrared (helping them catch their prey), and some insects can see ultraviolet (guiding them into flowers).
    These wavelengths are outside the 400-700nm range, i.e. humans can't see these things.
    What I'm interested to know is that when those reptiles see infrared, do they just see a dark red colour, or do they see some other colour, which us humans have no word for?
  8. Jun 17, 2011 #7


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    Or do those reptiles smell or feel infrared light. (since it is detected by pits on their nose)
  9. Jun 17, 2011 #8
    I think they see the colour 'food'.
  10. Jun 17, 2011 #9


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    good answer :)
  11. Jun 18, 2011 #10
    Thanks all .

  12. Jun 18, 2011 #11


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    We're able to distinguish different colors because we have 3 different types of cones (daytime light detectors) in our eyes, which are relatively sensitive to different parts of the visible spectrum. So our brain isn't only getting information about brightness, it also gets the information that -- for example -- the red cones are reacting more strongly than the green and blue cones, therefore this object I am seeing is red.

    (From http://wiki.umd.edu/wikivision/index.php?title=Color_blindness )​
    Last edited by a moderator: Apr 26, 2017
  13. Jun 18, 2011 #12
    As BRUCE W points out what is the color of infrared waves? Of course it is irrelevant to talk about color when we do not perceive it, but what if we suddenly got the capability of sensing low energy photons. Then what? What would be the color of infrared. lets give it a thought.
  14. Jun 18, 2011 #13
    According to what I said above, colour is the name we give to perceptions arising of excitations in the visual cortex. That can include colours in dreams: the component of the visual cortex responsible for the sensation is active. The component of the brain in dreaming or waking for perceiving that sensation is active.

    If there is no receptor for IF among the visual cells to send a signal to the component of the visual cortex responsible for colour sensations, there will be no 'colour' for IF. The concept has no meaning.
  15. Jun 18, 2011 #14
    I imagine colours will be expanded over the new range, so infrared would just be red.
    If we saw the whole frequency then gamma would be blue and radio red. Looking at the range of normal visible light, you wouldn't see much difference.
  16. Jun 18, 2011 #15
    Let's back up a little. 'Colour' is a mental construct. EM has no 'colour' whatsoever in any band of the spectrum, from VLF to gamma.

    If, over the course of time, people's low-frequency cone receptors shifted their sensitivity rightward on redbelly's scale above, all things being equal in the brain, IF would probably correspond with the sensation 'red'. But another possibility would be a mutant red cone-receptor developing parallel to the original and we would have 4 sensitivity bands, and 'red' would stay in its original place, and the mutant would excite the 'colour':

  17. Jun 18, 2011 #16


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    No. Red is interpreted because a particular molecule in the retina is chemically transformed by a particular frequency range of photons.

    To sense IR, we would have to have a different molecule, and it would be wired up to the brain differently, so it would not simply be an extrapolation of existing red.

    Same with UV.
  18. Jun 19, 2011 #17


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    I've noticed that I, and a few people I've run into, seem to observe things differently than most other people. I thought I was just a freak. But then again...

    There is a certain flower that grows wild in my area, that I've always been fascinated with. It seems to glow. For me at least. No one else seems interested in it.

    It doesn't really have a different colour. It simply glows differently.

    I wonder if this is why women are more flower prone than men?

    hmmm..... I think I'm straying outside of the OP. But then again, maybe not. Or perhaps this question belongs somewhere else? Or perhaps, like after so many other long days, I simply belong in bed?

    good night everyone. :zzz:
    Last edited by a moderator: May 5, 2017
  19. Jun 19, 2011 #18
    That's what I was saying, our brain would interpret IR as being the colour red.
    I just meant that if our eyes and brain had developed to see the whole spectrum, our current colour (what our brain sees) spectrum would be scaled to the new EM range.
    Unless of course it created new 'colours' to associate with different frequencies, that is if it possible for the brain to create more colours than it has already.
  20. Jun 19, 2011 #19


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    There is no reason to think this. The molecule that is linked to red does not respond to IR. The processes that turn frequency into colour know or care nothing about where on the spectrum a colour/frequency might fall (we know nothing of the "EM range"). Our brain does not know that green "falls between" red and blue, so there is no reason for our brain to interpret IR (if we had the receptors to do) as any more related to red than to, say, blue.
  21. Jun 19, 2011 #20
    So, then , the concept is that colour are the creative names given by our brain to the different frequencies we perceive. That means there are lots of different colours perceived by us but not distinguished. Then the brain may just create another colour for infrared which maybe much distinguishable or very less distinguishable.
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