Can light be filtered using red fabric?

  1. If I put a red fabric under the Sun, what can this fabric be filtered in term of light frequency spectrum?
    Thanks in advance of any suggestions
     
  2. jcsd
  3. Drakkith

    Staff: Mentor

    Are you asking the spectrum of light that passes through the cloth, reflects off of it, or what?
     
  4. I would like to know the spectrum of light passing through the cloth,
    since the Sunlight pass through the red cloth, will the red color of light or infrared be greater increase within the spectrum?
    Thanks everyone very much for any suggestions
     
  5. Vanadium 50

    Vanadium 50 17,740
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    No, a filter can only remove light, never increase it.
     
  6. The way I understand your question, The amount of red in the sunlight would be reduced
    by passing through a red cloth. A portion of the red spectrum would be reflected, and therefore not transmitted. In Practice, cloth would make a poor filter, as it has all sorts of
    irregular surfaces. A true red filter would reflect most of the red leaving the remaining spectrum.
     
  7. davenn

    davenn 3,675
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    huh ??
    you better reread optics 101 ;)

    all my optical filters of various colours that I use in photography PASS the colour of the filter and STOP other colours

    Another example... why do you think they use RED filters in front of IR receiver sensors ?
    ...so that the red end of the spectrum is passed and the rest of the spectrum is filtered out
    thereby avoiding false triggering and reduced sensitivity of the IR sensor

    Dave
     
  8. I would like to know the reason why IR receiver use IR within spectrum instead of other spectrum, does it have any specific property for IR?
    Thanks everyone very much for any suggestions
     
  9. davenn

    davenn 3,675
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    sorry I dont really understand your question
    care to rephrase ? :smile:


    Dave
     
  10. Chronos

    Chronos 9,975
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    If you look through a red filter, everything looks red. Like Dave said, the filter color is the light frequency that is unblocked.
     
  11. I am interested and would like to know more about why use RED filters in front of IR receiver sensors, and the reason to select IR instead of other spectrum on this receiver sensors device.

    Does anyone have any suggestions?
    Thanks everyone very much for any suggestions
     
  12. davenn

    davenn 3,675
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    I gave the answer in post #6 :smile:

    Dave
     
  13. ... and the reason to select IR instead of other spectrum on this receiver sensors device.

    Thanks everyone very much for any suggestions
     
  14. davenn

    davenn 3,675
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    1) cuz its invisible to the naked eye so you dont see the remote control transmitters flashing light all the time.
    2) Lighting up an area at nite time for camera survlence (sp?) doesnt flood the area with unwanted light
    3) IR is so much easier to filter than light within the visible spectrum

    Dave
     
  15. Drakkith

    Staff: Mentor

    Infrared light is used for various purposes, including remote controls, night vision, and to observe different things in space that are either blocked in the visible range or don't emit in the visible range. Do you know what the EM spectrum is?
     
  16. If I apply a red filter, are Infrared, Microwave and Radio passed? and are Gramma ray, X-ray, Ultraviolet, Visible filtered out?

    Does anyone have any suggestions?

    Thanks everyone very much for any suggestions


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    Last edited: Feb 22, 2012
  17. davenn

    davenn 3,675
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    I have already clarified visible light is filtered out other than the red end of the spectrum.
    Radio wavelengths ... microwave or otherwise and not filtered nor are Xrays or gamma rays
    Radio wavelengths ... microwave or otherwise you need a metallic screen --- basically a Faraday shield
    You can filter radio/microwave frequencies using a metallic screen where the holes in the screen are
    considerably less than a 1/4 wavelength in diameter...... look at the screen on the front of your microwave
    oven... the holes are large enough that we can see what's cooking but the 2.4 GHz radio energy cannot pass


    the RED filter of the topic IS AN OPTICAL FILTER !! :frown:



    Dave
     
    Last edited: Feb 22, 2012
  18. Drakkith

    Staff: Mentor

    This isn't easy to answer, it totally depends on the material. And is your signature set to ask for suggestions every post? It really doesn't make any sense.
     
  19. I understand Dave, I was thinking of type of red filter used in say HeNe laser safety glasses.
    They actually filter out the red light. It's been many years, but i recall they had a green tint to them. :)
     
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