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I Colored Light or Colored Object?

  1. May 3, 2018 #1
    Is it possible to modulate light as it is to modulate sound.?That is, taking "white" light and changing its color without using a filter or another object like a prism?
     
  2. jcsd
  3. May 3, 2018 #2

    berkeman

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    Welcome to the PF.

    Filtering a color out of white light is not modulation, it is just selectively filtering the many colors of white light to get one particulat color.

    Modulation has a technical meaning -- it means modifying a waveform in amplitude, phase or frequency:

    https://en.wikipedia.org/wiki/Modulation

    If you have a light wave or a sound wave propagating through your apparatus (pickup antenna, modulator, transmit antenna), you can do some things to it, but other things are harder. For example, amplitude modulating a sound wave or a light wave with such a setup is straightforward. Phase modulating them is harder, and frequency modulating them is very specialized if possible at all. (Assuming you mean just doing something to the propagating waveform, as opposed to converting it to electrical signals that you process and re-transmit with an antenna or transducer)

    Can you say more about the context of your question? That will help us to give you the best answers that we can. :smile:
     
    Last edited: May 3, 2018
  4. May 3, 2018 #3
    White light is what we see as a fairly evenly mixed wavelengths of light within the visible spectrum.
    Not surprising really since we evolved on Earth and the peak wavelengths of the Sun are in that range.
    The equivalent with sound would be 'white noise', a vague hiss comprising of many frequencies.
    It is possible to filter both light and sound so that some chosen frequencies are more or less apparent.
    That isn't modulation though. it's just cutting out the bits you don't want.
     
    Last edited: May 3, 2018
  5. May 4, 2018 #4

    sophiecentaur

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    Did you do a search on "Optical Modulators"? Does this question come from personal curiosity or did you have an application in mind?
    Light Modulation is more or less what the LCD cells in front of a conventional back lit LCD monochrome TV display do. The cells Modulate the Amplitude of the light.
    But modulating the amplitude is easy.
    Modulating the frequency of a beam of light is much harder. It is possible to 'mix' optical signals to produce a sum or difference frequency (it's much easier to achieve this with Radio Frequency signals and that's done in radio and TV receivers).
     
  6. May 4, 2018 #5
    Thanks everybody for the reactions. Here is what I mean as succinctly as possible.
    The theory says that white light (or sunlight if you prefer) is a mix of (all) colors. Beyond all the technicalities I wonder how that can be proven otherwise than by letting it through a prism like Newton did.
    As far as I know, colors from a tv screen for instance, come from Red Green Blue filters. That is, white light goes through these colored filters and get the color of the filter, and that is exactly what I find intriguing. Could it be possible, however that is done, to produce colors without those filters? I used the term modulation as an analogy, so please do not hold me to that term. The point is we can change how a sound sounds, can we then change the color of say a beam of light without letting it pass through filters which are already colored?
     
  7. May 4, 2018 #6

    berkeman

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    That's how a color LCD display works, but not how an LED display works... :smile:
     
  8. May 4, 2018 #7
    I am afraid I do not see how that is relevant. I do not know enough about the differences between both. Do you mean to say that LED screens already do what I am asking about? If so, I would be very curious how it is done.
     
  9. May 4, 2018 #8

    berkeman

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    Red, green and blue LEDs are used to generate the light. They do not start with white light and filter the light. So colored LEDs generate their colored light in a fundamentally different way compared to colored incandescent bulbs. And I thought that was what you were looking for... :smile:
     
  10. May 4, 2018 #9

    berkeman

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  11. May 4, 2018 #10
    It is certainly very interesting, but what I make of it still does not answer my question. I may be wrong but this is how I understand electro-luminescence. Crystals when put under electric current produce colored light. The color is apparently linked to the kind of crystal. If I am right, then it is the same thing as having white light going through a colored filer, only in the case of leds, it is the filters themselves that give off light?
    Did I understand it wrong?

    edit: it is somehow comparable (only an analogy!) to cathode rays. They all have different colors depending on the gases in the tube, right?
     
  12. May 4, 2018 #11

    berkeman

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    No, it is fundamentally different. Have you learned yet about how electron energy level transitions in atoms can give off photons?
     
  13. May 4, 2018 #12
    It would help if you explained how it is fundamentally different. The first thing that comes to mind are the black-body experiments that started the whole quantum adventure. But please let us keep to crystals and leds.
     
  14. May 4, 2018 #13

    berkeman

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    First can you say what you mean by "crystals"? Can you post some links to the reading you have been doing about crystals generating light? Thanks.
     
  15. May 4, 2018 #14
    The Wikipedia article in your previous posts. Again I apologize for my imprecise terminology, it refers to different materials used in the diodes. Here is a quote from this article:
    "
    220px-SiC_LED_historic.jpg
    Green electroluminescence from a point contact on a crystal of SiCrecreates Round's original experiment from 1907.
    Electroluminescence as a phenomenon was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat's-whisker detector
     
  16. May 4, 2018 #15
    Yes.
    Yes.
    Yes.

    And?
     
  17. May 4, 2018 #16
    You are not seriously expecting an answer?
     
  18. May 4, 2018 #17
    I was expecting a question,
     
  19. May 4, 2018 #18
    I have trouble taking your remark seriously, and I would not know how to respond without rehashing the whole thread.
     
  20. May 4, 2018 #19

    berkeman

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    Well, we are trying to help you, and trying to determine your background and level of knowledge.

    Please do some reading and then tell us why incandescent lights are fundamentally different from LED lights. That's a good start. Thanks.
     
    Last edited: May 4, 2018
  21. May 4, 2018 #20
    I have been reading for years on the subject, even though the last time I had formal lessons in Physics was in High school, in the 60's and 70's.
    I have read the article you kindly linked and gave my opinion. I take your remarks very seriously, but I cannot take any remark seriously, not when it shows a complete disregard of what has been written in the thread.
     
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