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Medical What colour absorbs radiant heat more?

  1. Jun 18, 2010 #1

    In regards with a black vs yellow t-shirt, which absorbs radiant heat from a indoor gas heater more? Or is the difference too small to tell? Sorry I don't own a yellow tshirt.

  2. jcsd
  3. Jun 18, 2010 #2
  4. Jun 18, 2010 #3

    Andy Resnick

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    The color of something is the visible waveband does not correlate well with it's 'color' in the infrared. Snow, for example, is black in the IR.

    It can be a little tricky to figure out- the incident power from the sun peaks in the green/yellow (555 nm), but the peak wavelength corresponding to (say) 90 deg. F (32 C) is around 9.5 microns. So a black shirt will absorb sunlight very well, but may also radiate the heat very well.

    For a gas heater, most of the radiant energy is around (IIRC) 3-5 microns. Again, the color in the visible has little to do with the optical properties in this waveband.

    As it happens, cotton cloth has an IR emissivity (8-12 microns) of about 0.8


    Close to the absorptivity in the visible. I couldn't find values for the mid-wave IR.

    What that means, in practice, is that the color of the fabric has very little effect on the thermal properties.
  5. Jun 18, 2010 #4
    Awesome, very informative, thanks.
  6. Jun 18, 2010 #5
    I always kind of assumed it was true that light colors reflected heat and dark colors absorbed heat, but I didn't really think about it. I have a white car that gets pretty hot sitting in the sun. Does it get just as hot as a black car? My dad has a dark red van and measured the heat on the paint to be pretty hot. He painted it white and measured it to be cooler than it was when it was dark red. I didn't see it and can't verify if it was conclusive. I'm just taking his word for it.
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