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Light and energy

  1. Jan 4, 2010 #1
    I am wondering if there is a significant loss in energy (greater than 2%) in light that is refracted through media. I also am wondering the same about energy loss in light that is focused via a parabolic lens.
     
  2. jcsd
  3. Jan 5, 2010 #2
    Normally incident light on a refracting media with index of refraction n from air with n=1, or from the same media to air, has a power loss of

    Power loss = (n-1)2/(n+1)2= 0.25/6.25 = 4% for glass with n=1.5.

    So for going through a glass lens without anti-reflection coating, the loss is about 8%. The loss in a front-surface parabolic mirror is near zero.

    Bob S
     
  4. Jan 5, 2010 #3

    tiny-tim

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    Hi Bob S! :smile:

    And (I' m guessing :blushing:) is it (n1-n2)2/(n1+n2)2 for general media?
     
  5. Jan 5, 2010 #4
    Is there energy loss in light that is focused via a parabolic lens?
     
  6. Jan 5, 2010 #5

    tiny-tim

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    uhh? Bob S :smile: just said so … about 8%.
     
  7. Jan 5, 2010 #6
    I said 0% using a front-surface-silvered parabolic mirror, 8% through a refracting glass lens.
    Bob S
     
  8. Jan 6, 2010 #7
    I'm not sure that 0% is correct. I know that even the best silvered dielectric mirros offer 99% reflection
     
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