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Light's reflection - wats ur perception?

  1. Nov 9, 2005 #1
    hi all
    one basic question in physics aroused owing to my poor memory.
    i vaguely remember that there is a difference in the colour of the object we see in reality and that generated by a television or for that matter any artificial source of light.
    1) Now how does our eye perceive these ( answer me in terms of wavelengths and in simple terms) ? and as we move away from an object do we perceive a change in the shade of the colour or not?
    2) Please tell me what role does light play ( is the perception affected by interference consider varying aperture of the eye) while we view images that are hazy ( technically passed thru low pass or high pass filters). i wud be happy if anyone cud answer using only the various phenomenon of light and without talking of filters and other engineering tools. please respond quickly. thank you.
  2. jcsd
  3. Nov 9, 2005 #2
    My understanding is the color we perceive is strictly related to the wavelength (or frequency if you prefer) of the light wave being transmitted to the signal receptors in our eyes. Therefore, an object that reflects a certain color at a certain wavelenth will appear the same as a TV set that can emit that color at the *exact same wavelenth*. If an object's color looks different after you record it and then view it on TV, it probably means the wavelength has been alterted slightly after the image is "processed" from the recording device through the CRT and onto your TV (which is a multistep process, all of which can lead to deviations from the original signal source). You can see how this happens by messing with the color control on your TV set (basically you are adjusting the internal settings in your TV so that it converts the incoming signal to the desired outgoing wavelenth...in theory if you synchronized them perfectly you could get a perfect outgoing image for the color your desired).

    It also depends on how sensitive your eyes are. For example, a color blind person might not percieve a color change at all even if the wavelength deviation is altered from the object to the TV set (if their eyes are not sensitive enough to pick up the change, the colors of the object and the TV will appear the same).

    If that's not good enough, I can always overwhelm you with sexy equations if you'd like :wink: Ignoring color, there are other differences between viewing real objects and images on TV (frame rate for example), but since you didn't ask about those...
  4. Nov 10, 2005 #3


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    I think this part of you question has to do with the cosmic redshift. Due to the Doppler effect, the wavelength of light is longer - redder - than when it was emitted at the source. If something emitting light is moving quickly away from an observer, the light will look redder. Blueshift is the opposite, if an object emitting electromagnetic radiation is quickly moving towards an observer, the light will look bluer.
  5. Nov 10, 2005 #4
    Its probably also worth noting, just to avoid confusion, that unless your planning on breaking the land speed record (well, every speed record thats ever existed) this isn't something your going to notice with your naked eye, or on a TV.
  6. Nov 10, 2005 #5


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    Oh yes, the speeds must be quite literally astronomical for any visible affects to occur.
  7. Nov 10, 2005 #6
    Don't know, might be a good idea to send your TV flying away from you at that speed :wink:
  8. Nov 10, 2005 #7

    Claude Bile

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    1) The colour you percieve depends on the wavelength (or more generally, the spectrum) of the light and nothing else (for the same person of course).

    2) I am not 100% clear what you are asking here. Varying the aperture in the eye alters the amount light we detect, which is why pupils dilate in darkness and so forth.

    Our eye works by focusing an image (via the lens) and on to the retina. When something appears hazy to us, it is because the image is not being focused onto the retina, it is being focused just before, or just after the retina.

  9. Nov 11, 2005 #8
    hi all

    thanks for ur replies......

    sorry for confusing u all earlier.

    it all started with a scenario i had on hand. here it goes.......
    i saw two images on my computer one angry and the other calm ( gray shades image). the moment i go back the expressions switch or even say i take off my glasses i am able to view the illusion. (this has nothing to do with cosmic shift pls!!!!!!) Now explain the phenomenon as a play of light.


  10. Nov 11, 2005 #9
    Could you post the images or links to them? That would make it a lot easier to give a good answer.
  11. Nov 13, 2005 #10

    Claude Bile

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    Sounds like an optical illusion - in that case, it is the wiring between your eyes and brain that is responsible for the effect and not the behaviour of the light itself.

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