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A few general questions about Optics

  1. Dec 17, 2009 #1
    Does light intensity change along with frequency? In other words, if you put the same voltage behind a white LED light and a blue LED light will the white light have a higher intensity or just a different frequency?

    Also, would shining a white light through a very clean thin colored filter change the intensity?

    Lastly, what would be required to converge different colored lights together? Do I just need a lens, or do I need a prism of some kind?

    If you have any links to where I can find out information like this, I would be most appreciative. I tried Google but nothing I found answered my questions. Until I get a book on optics, my thanks to whoever can help answer my questions.
  2. jcsd
  3. Dec 17, 2009 #2
    A white LED is a blue LED--a blue LED with a phosphor coating on the inside! Yep, the same kind of phosphor that coats the inside of a flourescent light. For this reason, the white LED will radiate fewer photons than the blue LED, as the phosphor in the white LED is somewhat lossy.
    If you were to compare a blue LED with a red LED (neither have phosphors in them), then yes, the blue led will radiate less light with the same current draw, because blue is a more energetic source of electromagnetic radiation.

    Shining white light thru a color filter will pass only that frequency that the color filter will not absorb. So while the passed frequency will not be decreased (just pretend we're using an ideal filter), all other frequencies get absorbed by the filter, thus the frequencies that get absorbed will be radically attenuated and lessened.

    If you're "converging" incoherent light (the kind of light coming from your LED, or a flourescent lamp), then using a lens to focus the different colors onto a white sheet of paper will very effectively blend them.

    One last thing I'll leave you with: research the Fabray/Perot interference/color filter. These filters have an extremely narrow bandwidth, and learning how these color filters work will give you a great lesson on color, light and interference in general. :smile:
  4. Dec 17, 2009 #3
    Thank you very much for the quick informative reply. You answered everything I asked and the questions I didn't think about asking! :biggrin:
  5. Dec 18, 2009 #4
    You're welcome. Now vote me in as Forum Science Advisor. :devil:
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