[LRflex] Re: Was a bunch of stuff, black fabric

To all seekers of truth:

See

http://www.straightdope.com/mailbag/mblackcool.html

http://www.newton.dep.anl.gov/askasci/gen01/gen01173.htm

All the best,

Bill


On Nov 26, 2006, at 7:06 PM, Aram Langhans wrote:

> OK David.  I am ready to tackle the black fabric question. Still  
> about 30
> message behind, though.
>
> I guess I really don't have an answer, or a guess like Colin, but I  
> do have
> a few thoughts.  The IR can only come from two sources.
> 1)  Light is being absorbed by the dark pigments and degraded to  
> heat and
> re-radiated.  This is happening in both non-synthetic and synthetic
> materials.
> 2)  Ambient IR is being reflected from the surfaces.  I assume this  
> is also
> happening to some extent from both fabrics.
>
> So, how to figure out what is going on.  I could suggest two possible
> experiments.
>
> 1.  Find some synthetic and non-synthetic black material that when
> photographed with film or read with a light meter give the same black
> readings.  They absorb the same amount of visible light.  Now  
> photograph
> them in a very cold room (walk in freezer or outside on a day like  
> today)
> and see what the results are.  Maybe synthetics re-radiate at a  
> different
> wavelength than non-synthetics?
>
> 2.  Using an IR flash, photograph them in total darkness to see if  
> there is
> any difference in what they reflect.  Maybe synthetics reflect more  
> IR than
> non-synthetics.
>
> I do not think there is any reason to believe that just because an  
> object is
> black it behaves the same as far as absorbing or reflecting in the  
> IR range.
>   Some materials may be very good at absorbing visible and IR, and  
> others
> only visible.
>
> I don't have an IR flash nor do I have an M8 to try these.  Also
>
>

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