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Yellow light through a prism

  1. Oct 10, 2012 #1
    I want to know that if yellow light pass through a prism will it spit into red and green light?:confused:

    I don't have prism and I need to know it soon. Thank very much.:smile:
  2. jcsd
  3. Oct 10, 2012 #2
    Impossible to know without applying the prism or some other spectral splitter to the specific source of yellow light.

    Man sees colour by perceiving excitation of 3 colour receptors - red, green and blue.

    All of them have wide absorption bands, and they overlap. Red receptor also has another absorption maximum in violet.

    The perception of yellow colour may be caused by a monochromatic light which excites both red and green receptors whose absorption spectra overlap in yellow. Such as sodium lamps, monochromatic at 589 nm.

    But mixture of, say, some light at 500 and some light at 700 nm would also excite both of these receptors, and if the lights are in suitable amounts then it can leave perception of yellow which the eye of man has no way to tell apart from the monochromatic light at 589 nm.

    A prism or other object with chromatic dispersion, like diffraction grating, would show the difference - monochromatic yellow would not be split, polychromatic would be split.
  4. Oct 10, 2012 #3
    So yellow light that is a mixture of red and green can be split back into red and green using prism?
  5. Oct 10, 2012 #4
    There are lots of combinations that would look like "yellow light" to a human. If you mean light which is purely in the yellow part of the spectrum (eg. a sodium lamp) then it would not split at all. If you mean sunlight, this will split into the entire visible spectrum. The human eye is not perfect!
  6. Oct 10, 2012 #5
    I mean if I mix red beam laser and green beam laser to make single beam yellow laser(about 580 nm) will it split?
    Last edited: Oct 10, 2012
  7. Oct 10, 2012 #6
    The wavelengths would not simply average out to yellow. You'd just have red and green light travelling along the same path without interfering, let's say 480nm and 680nm. Since their refractive indices are different, it would split. But you wouldn't find any 580nm light anywhere along either beam.
  8. Oct 10, 2012 #7
    thank so much.

    Another question, can pure yellow light pass through a green filter?
    Last edited: Oct 10, 2012
  9. Oct 10, 2012 #8
    No, assuming the filter is ideal (in reality it is probably not 100% opaque to yellow light).
  10. Oct 10, 2012 #9
    When is a "green filter" "ideal"? What is "ideal" about it?

    For example, say that you have a filter that passes 100 % of any light between 500 and 600 nm, and 0% of any light either longer than 600 nm or shorter than 500 nm.

    Quite "ideal" behaviour.

    It would probably look green in passed white light.

    But it would pass pure yellow light at 590 nm just as completely as a pure light at 510 nm.
  11. Oct 10, 2012 #10


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    Bringing lasers into it is adding a further complication. Any good (reasonably 'monochromatic') light sources would do. Through any optical system they will remain totally separate - not affecting each other or mixing in any way. So we can pass them through a prism, split them and then re-combine them and split them again ad infinitum. AS IT HAPPENS, our eyes have a very crude system for assessing the combinations of wavelengths of light that they receive. (Don't take this personally! We all enjoy the 'colours' we see but that's to do with our brains). We cannot distinguish between a combination of two light sources with long and short wavelengths and a single wavelength somewhere in the middle. Our three receptors can appreciate many different combinations of wavelengths and we 'interpret' these combinations as being different colours.
    To clear things up a bit and to be a bit pedantic, one should really not talk of a "light with a red wavelength". One should, strictly, say "light with a wavelength that we see as red". This is consistent with the fact that other (infinite possibilities of) combinations of different wavelengths are seen as different colours.
    If it weren't for this quirky fact about our colour vision, colour TV would need to be a lot more complex than just needing three colour channels -RGB.
  12. Oct 10, 2012 #11
    thank you
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