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Downgoing & Upgoing radiant heat equally reflected by RB?

  1. Jun 30, 2015 #1
    I'd read that "Most solar energy has a wavelength close to 0.5 µm" and that
    "All surfaces radiate heat, mostly at wavelengths close to 10 µm wavelength."


    So, just to confirm, that means that a black roof in the clear summer sun is heating up primarily as a result of the wavelengths as seen under most of the red above and later whatever that hot roof is re-radiating away that night will be in wavelengths mostly under the blue, correct?

    OK, so here's my question, does common radiant barrier, like the aluminum foil faced rolls you see for sale that claim a 95% reflectance, do they equally reflect radiant heat at both 0.5 µm and 10 µm wavelengths? If not, how significantly so do they not?

    If RB does not reflect both equally, I'll have a follow up question.

    Thank you for any responses.
  2. jcsd
  3. Jun 30, 2015 #2
    Looking more now, I see I may have the answer to my question here...

    ...that is if all my other earlier assumptions were correct without major qualifiers being brought up by anyone.
    Which I eagerly invite, if there are any.

    Point of my asking the question was to be sure commonly available aluminum radiant barrier was close to equally reflective of radiant heat in the wavelengths originating from both direct sunlight and for radiant heat wavelengths radiating from objects and building materials, too. It looks like it is, unless I'm missing something else here.

    Any comments?
  4. Jun 30, 2015 #3


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    Staff: Mentor

    Aluminum should do well at reflecting most wavelengths you're interested in. I can't vouch for the radiant barriers, which probably won't be quite as reflective as the graph shows, but it should be close enough for any common uses.
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