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Why is there a peak in the visible range?

  1. Sep 17, 2013 #1
    I have always wondered why the intensity of the graph always peaks in the visible portion of spectrum.

    http://3.bp.blogspot.com/-fOnjOBanbcw/TqG1dI81fnI/AAAAAAAABpM/mRL5kfi-i_Y/s1600/ThermalRadiation.png

    I understand that the graph represents intensity does not continually increase as wavelength approaches 0, but is there any significance or particular reason for the peak on this graph to be around the visible range of wavelength or is it just a coincidence?
     
  2. jcsd
  3. Sep 17, 2013 #2

    phyzguy

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    Note that as T decreases, the peak moves out of the visible range and into the infrared, so it doesn't "always" peak in the visible range. The radiation from the cosmic microwave background, for example, peaks in the microwave region. The reason the radiation from the sun peaks in the visible range is that our eyes have evolved to see the light that is most intense in the solar spectrum.
     
  4. Sep 17, 2013 #3

    D H

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    Staff Emeritus
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    We see in the visible range precisely because that's where sunlight is most intense. The eye evolved to take advantage of that peak lighting. Creatures on a planet orbiting a smaller, redder star would most likely see into the near infrared, but may not be able to see violet or blue.
     
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