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Re: [Hammock Camping] Radiation/absorption question

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  • Randy Saylor
    I have never believed that the color of material that is in contact with your skin makes much difference because conduction, not radiation, will be the main
    Message 1 of 12 , Oct 29, 2004
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      I have never believed that the color of material that is in contact with your skin makes much difference because conduction, not radiation, will be the main method for heat transfer. I agree that a dark bag liner will dry faster than a light one and that is due to better absorption of light energy.
       
      Hot water radiators in homes work most efficiently if painted black, or at least a dark color.
       
      Why are polar bears white? Is it to reduce radiation or give good camouflage? Probably for both reasons.
       
      Randy
       
       
      ----- Original Message -----
      Sent: Friday, October 29, 2004 8:41 PM
      Subject: Re: [Hammock Camping] Radiation/absorption question


      Well, I think I understand the theory but probably not well enough to
      explain it so that you will understand it.  Basically, you only need
      a dark surface so that you can dry a damp bag quicker in sunlight.

      First, lighter colors are better reflectors, poorer absorbers and
      poorer radiators than darker colors.

      As far as thermal efficiency for a sleeping bag, you would want both
      the inner and outer surface to be a light color.  You would want the
      inner suface to be a good reflector/bad absorber so that you would
      maintain more of your body heat instead of warming your sleeping
      bag.  You would want the outter surface to be a poor radiator so that
      the heat that you did put into the bag would stay in the bag and not
      efficiently radiate heat to cooler outside objects, like your tent,
      tarp, clouds or worse yet, the open sky.

      Radiant heat transfer requires physical seperation, is inversely
      proportional to (distance)^2 and directly proportional to
      (temperature difference)^4 of the objects involved with the radiant
      heat transfer.  When the other object is your tarp or tent there
      probably isn't a whole lot of radiant heat transfer going on and the
      difference in fabric color isn't so much, but this might be more of a
      factor with a clear night sky.  Where you will definately see a big
      difference is in bright sunlight and this is why you want a dark
      color to quicken the drying time for a damp bag.  If I was going to
      pick which surface to make dark for solar drying, it would be the
      inner surface... my thinking is that most of it will be in contact
      with you and the heat transfer will primarily be by conduction, not
      radiation.

      I told you my explanation might not make any sense.

      Youngblood

      --- In hammockcamping@yahoogroups.com, Aris Dennis <apfel1984@y...>
      wrote:
      > I've never understood the theory;
      > You're using the quilt at night, so theres no light
      > around anyway- why would colours make any difference
      > at night?
      > Aris
      >
      >
      >
      > --- Randy Saylor <r.saylor@s...> wrote:
      >
      > > A dark exterior will radiate heat away from the
      > > hammock and thus the body inside it. White would be
      > > the best exterior colour to prevent radiation.
      > > Randy
      > >   ----- Original Message -----
      > >   From: jwj32542
      > >   To: hammockcamping@yahoogroups.com
      > >   Sent: Friday, October 29, 2004 7:30 PM
      > >   Subject: [Hammock Camping] Radiation/absorption
      > > question
      > >
      > >
      > >
      > >   I think I'm misunderstanding why some bags/quilts
      > > have light
      > >   outsides and dark insides.  I know it's for
      > > radiation, but here's
      > >   where I'm confused.
      > >
      > >   Light colors radiate heat and dark colors absorb
      > > heat.  So wouldn't
      > >   you put the light color on the inside to radiate
      > > the heat back at
      > >   your body?  And the dark color on the outside to
      > > absorb ambient heat
      > >   into the bag, keeping you warmer?
      > >
      > >   If the inside is dark, then the bag is absorbing
      > > and storing your
      > >   body heat rather than letting your body use it.
      > > And the light outer
      > >   layer is reflecting ambient heat back into the
      > > atmosphere instead of
      > >   storing it in your bag.
      > >
      > >   So which is right?
      > >
      > >   Jeff
      > >
      > >
      > >
      > >
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    • Ralph Oborn
      The contact comment was refering to metalic foils etc. Sorry if it wasn t clear. Ralph
      Message 2 of 12 , Oct 29, 2004
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        The contact comment was refering to metalic foils etc. Sorry if it wasn't clear.

        Ralph


        On Fri, 29 Oct 2004 21:39:15 -0400, Randy Saylor <r.saylor@...> wrote:
        >
        > I have never believed that the color of material that is in contact with
        > your skin makes much difference because conduction, not radiation, will be
        > the main method for heat transfer. I agree that a dark bag liner will dry
        > faster than a light one and that is due to better absorption of light
        > energy.
        >
        > Hot water radiators in homes work most efficiently if painted black, or at
        > least a dark color.
        >
        > Why are polar bears white? Is it to reduce radiation or give good
        > camouflage? Probably for both reasons.
        >
        > Randy
        >
        >
        >
        >
        >
        > ----- Original Message -----
        > From: Dave Womble
        > To: hammockcamping@yahoogroups.com
        > Sent: Friday, October 29, 2004 8:41 PM
        > Subject: Re: [Hammock Camping] Radiation/absorption question
        >
        >
        > Well, I think I understand the theory but probably not well enough to
        > explain it so that you will understand it. Basically, you only need
        > a dark surface so that you can dry a damp bag quicker in sunlight.
        >
        > First, lighter colors are better reflectors, poorer absorbers and
        > poorer radiators than darker colors.
        >
        > As far as thermal efficiency for a sleeping bag, you would want both
        > the inner and outer surface to be a light color. You would want the
        > inner suface to be a good reflector/bad absorber so that you would
        > maintain more of your body heat instead of warming your sleeping
        > bag. You would want the outter surface to be a poor radiator so that
        > the heat that you did put into the bag would stay in the bag and not
        > efficiently radiate heat to cooler outside objects, like your tent,
        > tarp, clouds or worse yet, the open sky.
        >
        > Radiant heat transfer requires physical seperation, is inversely
        > proportional to (distance)^2 and directly proportional to
        > (temperature difference)^4 of the objects involved with the radiant
        > heat transfer. When the other object is your tarp or tent there
        > probably isn't a whole lot of radiant heat transfer going on and the
        > difference in fabric color isn't so much, but this might be more of a
        > factor with a clear night sky. Where you will definately see a big
        > difference is in bright sunlight and this is why you want a dark
        > color to quicken the drying time for a damp bag. If I was going to
        > pick which surface to make dark for solar drying, it would be the
        > inner surface... my thinking is that most of it will be in contact
        > with you and the heat transfer will primarily be by conduction, not
        > radiation.
        >
        > I told you my explanation might not make any sense.
        >
        > Youngblood
        >
        > --- In hammockcamping@yahoogroups.com, Aris Dennis <apfel1984@y...>
        > wrote:
        > > I've never understood the theory;
        > > You're using the quilt at night, so theres no light
        > > around anyway- why would colours make any difference
        > > at night?
        > > Aris
        > >
        > >
        > >
        > > --- Randy Saylor <r.saylor@s...> wrote:
        > >
        > > > A dark exterior will radiate heat away from the
        > > > hammock and thus the body inside it. White would be
        > > > the best exterior colour to prevent radiation.
        > > > Randy
        > > > ----- Original Message -----
        > > > From: jwj32542
        > > > To: hammockcamping@yahoogroups.com
        > > > Sent: Friday, October 29, 2004 7:30 PM
        > > > Subject: [Hammock Camping] Radiation/absorption
        > > > question
        > > >
        > > >
        > > >
        > > > I think I'm misunderstanding why some bags/quilts
        > > > have light
        > > > outsides and dark insides. I know it's for
        > > > radiation, but here's
        > > > where I'm confused.
        > > >
        > > > Light colors radiate heat and dark colors absorb
        > > > heat. So wouldn't
        > > > you put the light color on the inside to radiate
        > > > the heat back at
        > > > your body? And the dark color on the outside to
        > > > absorb ambient heat
        > > > into the bag, keeping you warmer?
        > > >
        > > > If the inside is dark, then the bag is absorbing
        > > > and storing your
        > > > body heat rather than letting your body use it.
        > > > And the light outer
        > > > layer is reflecting ambient heat back into the
        > > > atmosphere instead of
        > > > storing it in your bag.
        > > >
        > > > So which is right?
        > > >
        > > > Jeff
        > > >
        > > >
        > > >
        > > >
        > > > Yahoo! Groups Sponsor
        > > > ADVERTISEMENT
        > > >
        > > >
        > > >
        > > >
        > > >
        > > >
        > > --------------------------------------------------------------------
        > ----------
        > > > Yahoo! Groups Links
        > > >
        > > > a.. To visit your group on the web, go to:
        > > > http://groups.yahoo.com/group/hammockcamping/
        > > >
        > > > b.. To unsubscribe from this group, send an
        > > > email to:
        > > > hammockcamping-unsubscribe@yahoogroups.com
        > > >
        > > > c.. Your use of Yahoo! Groups is subject to the
        > > > Yahoo! Terms of Service.
        > > >
        > > >
        > >
        > >
        > >
        > >
        > > __________________________________
        > > Do you Yahoo!?
        > > Take Yahoo! Mail with you! Get it on your mobile phone.
        > > http://mobile.yahoo.com/maildemo
        >
        >
        >
        >
        >
        >
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        >
        > ADVERTISEMENT
        >
        >
        > ________________________________
        >
        >
        > Yahoo! Groups Links
        >
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        >
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        >
        > Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
      • Craig Everhart
        Hi, I m, Craig - just started on this site. am interested in hammock camping and want to learn. White polar bears have puzzled me for a long time. Camouflage
        Message 3 of 12 , Oct 29, 2004
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          Hi,
          I'm, Craig - just started on this site. am interested
          in hammock camping and want to learn.

          White polar bears have puzzled me for a long time.
          Camouflage seems like one good reason.

          I picked up somewhere that white fur also allows light
          to reflect inward to the skin. That made some sense
          too.

          I guess next time I see a polar bear I'll ask. :-)


          > Why are polar bears white? Is it to reduce radiation
          > or give good camouflage? Probably for both reasons.
          >
          > Randy




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        • Dave Womble
          Ralph, I have this figured differently than you. I believe that darker materials are better at both absorbing and emmitting radiant heat. Youngblood
          Message 4 of 12 , Oct 30, 2004
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            Ralph,

            I have this figured differently than you. I believe that darker
            materials are better at both absorbing and emmitting radiant heat.

            Youngblood

            --- In hammockcamping@yahoogroups.com, Ralph Oborn <Ralph.oborn@g...>
            wrote:
            > You would also want it darker (better absorbing) in the infrared. If
            > it is bright (emmittive) in the IR then even at night you are losing
            > energy (warmth). IR reflectors (foils) will slow it down, unless you
            > are touching it then it is conductive heat transfer.
            >
            > Ralph Oborn
            >
            >
          • Dave Womble
            Opps, maybe not. I think we are saying the same thing... I didn t read it carefully enough. Sorry, Youngblood ... ... If ... losing ... you
            Message 5 of 12 , Oct 30, 2004
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              Opps, maybe not. I think we are saying the same thing... I didn't
              read it carefully enough.

              Sorry,
              Youngblood

              --- In hammockcamping@yahoogroups.com, "Dave Womble" <dpwomble@y...>
              wrote:
              >
              > Ralph,
              >
              > I have this figured differently than you. I believe that darker
              > materials are better at both absorbing and emmitting radiant heat.
              >
              > Youngblood
              >
              > --- In hammockcamping@yahoogroups.com, Ralph Oborn
              <Ralph.oborn@g...>
              > wrote:
              > > You would also want it darker (better absorbing) in the infrared.
              If
              > > it is bright (emmittive) in the IR then even at night you are
              losing
              > > energy (warmth). IR reflectors (foils) will slow it down, unless
              you
              > > are touching it then it is conductive heat transfer.
              > >
              > > Ralph Oborn
              > >
              > >
            • Randy Saylor
              This is tricky stuff. Consider light energy absorption. A black surface is black because it absorbs the light and does not reflect it. A pure white surface
              Message 6 of 12 , Oct 30, 2004
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                This is tricky stuff. Consider light energy absorption. A black surface is black because it absorbs the light and does not reflect it. A pure white surface reflects all the light and absorbs very little. Therefore the black surface will get warmer. Thus dark clothing will make us hot in bright sunshine more so than light clothing.
                 
                Now emission or radiation is different. A warm body will emit heat energy in the form of infra red radiation. Also it will lose heat by conduction to material it is in contact with. Conduction is affected more by the nature of the material (metal vs cloth, for example) than it is by the color of the material. If a gas (air) or liquid is in contact with the warm body then the heat will conduct away and then be removed by convection. The color makes a difference with radiation where the black body will radiate infra red more efficiently. In a hammock, limiting conduction is the most critical factor and thus all the effort to provide an insulating barrier.
                 
                This is how I understand this topic and I would welcome any clarification.
                 
                Randy 
                ----- Original Message -----
                Sent: Saturday, October 30, 2004 7:38 AM
                Subject: Re: [Hammock Camping] Radiation/absorption question


                Opps, maybe not.  I think we are saying the same thing... I didn't
                read it carefully enough.

                Sorry,
                Youngblood

                --- In hammockcamping@yahoogroups.com, "Dave Womble" <dpwomble@y...>
                wrote:
                >
                > Ralph,
                >
                > I have this figured differently than you.  I believe that darker
                > materials are better at both absorbing and emmitting radiant heat. 
                >
                > Youngblood
                >
                > --- In hammockcamping@yahoogroups.com, Ralph Oborn
                <Ralph.oborn@g...>
                > wrote:
                > > You would also want it darker (better absorbing) in the infrared.
                If
                > > it is bright (emmittive) in the IR then even at night you are
                losing
                > > energy (warmth). IR reflectors (foils) will slow it down, unless
                you
                > > are touching it then it is conductive heat transfer.
                > >
                > > Ralph Oborn
                > >
                > >




              • zippydooda
                Youngblood, you are correct. So, you paint your radiators black, since you want for the heat to get out of them. But, you use a brightly polished teakettle
                Message 7 of 12 , Oct 31, 2004
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                  Youngblood, you are correct. So, you paint your radiators black,
                  since you want for the heat to get out of them. But, you use a
                  brightly polished teakettle (or light colored, I guess), because it
                  keeps the heat in.

                  At night, the outside surface of your peapod (or underquilt) is
                  warmer than the surroundings, so you want to try to keep that heat
                  in. So, you use a light color or even a reflective cover. If you
                  make it dark, you will radiate more heat. You can't soak up heat at
                  night with a dark peapod, because heat has to move from hotter to
                  colder items (it's a law).

                  Like others said, the color of the inside of the bag doesn't matter
                  too much, since it's more of a conductive thing going on there. So
                  black would be nice since it hides dirt and makes it easier to dry
                  your bag in the sun.

                  All this radiation stuff works the same with heat flowing the other
                  way, too, right? Dark stuff gets hotter in the sun than light
                  stuff. The color of a surface (or whether it is rough or polished,
                  in the case of metal) influences heat going both in and out.

                  Hopefully this makes sense.

                  Bill in Houston


                  --- In hammockcamping@yahoogroups.com, "Dave Womble" <dpwomble@y...>
                  wrote:
                  >
                  > Ralph,
                  >
                  > I have this figured differently than you. I believe that darker
                  > materials are better at both absorbing and emmitting radiant heat.
                  >
                  > Youngblood
                  >
                  > --- In hammockcamping@yahoogroups.com, Ralph Oborn
                  <Ralph.oborn@g...>
                  > wrote:
                  > > You would also want it darker (better absorbing) in the infrared.
                  If
                  > > it is bright (emmittive) in the IR then even at night you are
                  losing
                  > > energy (warmth). IR reflectors (foils) will slow it down, unless
                  you
                  > > are touching it then it is conductive heat transfer.
                  > >
                  > > Ralph Oborn
                  > >
                  > >
                • dlfrost_1
                  ... camouflage? Probably for both reasons. The hairs of a Polar Bear are almost clear and are hollow. The white appearance comes from the even scattering of
                  Message 8 of 12 , Oct 31, 2004
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                    --- In hammockcamping@yahoogroups.com, "Randy Saylor" <r.saylor@s...>
                    wrote:
                    > Why are polar bears white? Is it to reduce radiation or give good
                    camouflage? Probably for both reasons.

                    The hairs of a Polar Bear are almost clear and are hollow. The white
                    appearance comes from the even scattering of light and is vital for
                    camouflage, as these animals are mainly ambush hunters. Because of
                    the internal scattering, the fur is also efficient at absorbing
                    infrared warmth from the sun. Their skin is dark back to protect
                    against UV light. (This why you see black around the eyes and nose--
                    the fur is thinnest there.)

                    Doug Frost
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