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Is chlorophyll green or green?

  1. Dec 16, 2013 #1

    kmm

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    Is chlorophyll "green" or green?

    Something I can't find a precise answer on is if chlorophyll reflects only green light. Each color has an associated wavelength, but as shown in a CIE chromaticity diagram, you can combine different wavelengths of light to create the perception of a single wavelength of light. So, is chlorophyll "green" or green?
     
  2. jcsd
  3. Dec 16, 2013 #2
    Chlorophyll reflects most strongly in what corresponds to the green and greenish range of monochromatic spectrum. Its absorption maximum is in the blue range, and the second maximum in the red range. But even at the maxima, it reflects somewhat. So the spectrum of the reflected light will depend on the spectrum of the incident light.
     
  4. Dec 16, 2013 #3
    Do a google image search for "chlorophyll absorption spectrum." You'll see a bunch of graphs showing what voko described.
     
  5. Dec 16, 2013 #4

    russ_watters

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    Also, you have the wrong idea about color. Light is a continuous spectrum: color is a concept invented by our eyes and brains. What we see as color is a combination what our three receptors see.
     
  6. Dec 16, 2013 #5

    kmm

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    I see now, thanks gor the responses.

    No I don't, I understand that our eyes and brains are what create the color we see, which is why I started the post. That's why I made the distinction between "green", which is what our eyes and brains create, and green as a single wavelength that our eyes and brains would also perceive as green.
     
  7. Dec 16, 2013 #6

    sophiecentaur

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    I, also, think that you do not fully understand what is meant by the word Colour.

    If you are saying that green is a single wavelength of monochromatic light (i.e. a spectral colour) then Chlorophyl definitely is not that green. i.e. it is not a spectral colour.

    We just describe it as 'a' green but our eyes are not spectrometers and there are many alternative ways of producing a good match to the green of Chlorophyl which do not have the same spectrum.

    And, BTW, there is no way of producing exactly the same colour response to any spectral colour, using any combination of other colours - spectral or otherwise. the spectral colours lie on a curve on the CIE chart and you can only produce a match if it lies on a straight line between the two other colours. In other words, a cord is always inside a curve.
     
  8. Dec 16, 2013 #7

    kmm

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    I understand all of that. I have probably been too general with some of my wording. I understand there are actually different frequencies for different hues of green so there's really no single green frequency. So I meant frequencies only in hues of green. What I was ultimately asking was if there were freqencies of other hues of different colors reflected by chlorophyll as well. Intuitively I was pretty sure that was the case. I'm not sure why I didn't think to look up the absorption spectrum.
     
  9. Dec 16, 2013 #8
    You can produce something with identical hue (which is what many people understand by color) but different saturation.
     
  10. Dec 16, 2013 #9

    sophiecentaur

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    OK - if you want to redefine terms. But, in my book, saturation counts and most people would not put up with a desaturated version of their favourite 'colour'.
     
  11. Dec 17, 2013 #10

    sophiecentaur

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    On the subject of the word 'hue', it is clearly wrong to think that a hue has a wavelength - or even an associated wavelength - because there are millions of 'colours' / 'hues' that lie on the CIE chart, the other side of the white point from spectral colours. There is no spectral colour which will match any of these. As with most of Science, it is always better to stick to the right terms and to use them in the accepted way, whenever possible, if you want to avoid confusion.
     
  12. Dec 17, 2013 #11

    kmm

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    I see. My thought on that was "green", "red", and "blue" are said to lie on a range of frequencies. Green is between the wavelengths of 490nm-560nm. When I look at this picture http://en.wikipedia.org/wiki/File:Rendered_Spectrum.png it looks to me that in the range of 490nm-560nm, the "greens" aren't quite the same, wouldn't those be different hues then, or am I misunderstanding?
     
  13. Dec 17, 2013 #12

    kmm

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    Actually, I think I see where I was wrong. Those different wavelengths that we would call green are all a part of a single hue..
     
  14. Dec 17, 2013 #13

    russ_watters

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    That's fine to think of that range of frequencies as being the "green range", yes - as long as that means you recognize the three errors in your first post and how they impact the answer to the question you asked. Because the way you said that implies you don't think there were any errors.
     
  15. Dec 17, 2013 #14

    kmm

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    I see how in my first post, what I said had the error of saying green has a single wavelength. I guess it isn't clear to me what the other errors are.
     
  16. Dec 17, 2013 #15

    sophiecentaur

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    and as long as you realise that there are many (the majority, in fact) 'greens' that are not pure spectral colours but a mix of other wavelengths. A very pale green, will have very nearly as much of all other wavelengths as those in the 'green' region of the spectrum. Look at the highly over-priced shades of white that some paint companies market. We'd all agree they're basically green but . . . . .

    The 'blue' sky is a very good example of a blue which we would describe as strong blue, under some circumstances (sun-drenched beaches or high in the mountains) but which is nowhere near 'spectral blue'. Look at the photographs of your holiday with your photo processing app and see what the RGB values are, for a very blue patch of sky. They certainly have a have significant amounts of R and G, as well as B.
     
  17. Dec 17, 2013 #16

    kmm

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    Thanks for helping me clear things up. When we see an object that appears green or blue, it is safe to assume that the frequencies under 'spectral blue' or 'spectral green' are the dominate frequencies though, correct?
     
  18. Dec 17, 2013 #17

    sophiecentaur

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    That's fair enough, yes.
     
  19. Dec 17, 2013 #18

    russ_watters

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    Dominant, but not by as much as you may think.

    A photo editor will give you the breakdowns of Red, Green and Blue that it mixes together to get a particular color. I threw in a medium dark photo of clear blue sky and got 97, 173 & 205 (max value 255).
     
  20. Dec 17, 2013 #19

    kmm

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    I wouldn't have expected that! I haven't really thought a lot about colors until now, just the very basics, so all of this is opening up a whole new world for me.. Physics is good at fooling my intuition :)
     
  21. Dec 17, 2013 #20

    sophiecentaur

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    There are very few, if any, sources of really saturated colour in everyday life. Laser pens and displays are more commonly seen these days and they are pure. Of course, there are the phosphors (or equivalent) in TV displays, which are as pure as the requirement for brightness and efficiency will allow. People think of the Rainbow as full of 'pure' colours. Look at a photo of a rainbow in a photo editor and look at the RGB values. Again, that's counter-intuitive until you realise its against a sky which already contains a hefty portion of R,G and B.
     
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