A little bit more to add, but first obviously Don means 300,000 kph or
186,000 mph for the speed of light, and includes all others except for Audio
which is ~742 mph.
The electromagnetic wave spectrum starts at Audio (0 Hz, though you
generally don't hear <20, to 20 KHz) then goes through Radio (20 KHz
-300,000 MHz), Micro, Infrared (heat), Visible Light, Ultraviolet, X, Gamma,
Cosmic. Wavelength starts at infinity and shortens as frequency increases.
Don is correct about infrared radiation and absorption but I believe it is
not so much color (light spectrum starting at the low freq/long wavelengths
Red Orange Yellow Green Blue Indigo Violet or ROY G BIV to remember it, also
used for color coding resistors, when they were still discrete components
:-) as much as lightness/darkness of the color (intensity? or whatever it's
called), White being lightest and Black darkest. Don, how about trying a
light and dark car of the same color, or shades of grey? :-)
I studied this in trying to determine which color on an amp in the trunk
radiated heat faster, black or white, since there would be no light
absorption but instead heat radiation. Turns out it would make more of a
difference of what kind of finish (brushed/anodized vs. heavy paint coated)
was on it, paint being an insulator vs. bare metal.
I suspect that is what Phil and Tony are experiencing between chrome/bare
steel vs. a painted surface, the heat conductivity of the metal, since
silver is a relatively light color. This does not diminish the white/black
factor. Hope this off topic gave you some knowedge to use somewhere.
Gary Lin
took some science classes, general science nut who baffled roommates by
sloshing ice in just washed ceramic cereal bowls because I hated warmed milk
Don Kerr enlightened and warmed us with:
> Dear Sir. Whilst I'm not a Physics Major,here are some FACTS.
> Sun radiation is a form of energy in its most pure form. It has visible
> and invisible spectrums.
> Light we see is composed of photons which travel at 300,000kph per second
> or 186,000 mph. (From the sun to us in 8 mins, that's 93,000,000 miles).
> What heat we feel is mostly caused by the infra-red spectrum. The heat
> from an object near you that you can feel is mostly radiant heat.
> Radiation being energy gives up that energy when it's absorbed.
> Actually it is a bit more complicated than this, but this is not Physics
> 101.
>
> Due to the reflective qualities of different surfaces,some heat up more
> than others.
> Black, especially matt black absorbs nearly all radiation, if it absorbed
> all without reflecting any, that object would be invisible. However an
> outline or blur would be seen due to light not passing through it to get
> to your eyes, so technically it would still be kind of visible, like a
> black hole. So invisibility is not possible in this dimension.
> So the amount of energy that is reflected from a surface determines its
> temperature. Black is hotter than White because White reflects more of the
> energy.
> We will not go into the non visible spectrum here ( ie, x-rays, gamma
> rays, ultra-violet, etc.)
> as that is another issue all together, although they too are energy and
> heat objects they strike or pass through, such as your micro-wave oven.
> My own observations with an infra-red heat sensor are these.
> Mid summer day at 2pm, no clouds, here in Oklahoma, subject vehicles
> outside all day from sun rise.
>
> Ambient temperature..................................104 deg F
> Humidity.............................................83% relative
> Black car roof.......................................176 deg F
> White van (VW transporter)............................124 deg F
> Red car..............................................148 deg F
> Black top road surface...............................179 deg F
> 15 inches above black top road in free, still air....123 deg F
> Thermal temperature sensor...........................Raytek Raynger ST2L.
>
From around 140 deg F up, this temperature on an object is uncomfortable to
the touch. Vinyl car seats were measured on the same day at 181 deg F in a
closed car. Plenty for 2nd degree burns on bare skin.
> Coffee you'll remember is around 160/170 deg when served, wanna keep your
> finger in it?
>
> I hope this clarifies your question about white buildings, Phil
> ............DK
>
> Tony Clark wrote:
> > Phil Ethier comments:
> > > Oddly enough, shiny metal seems to heat in the sun more than
> white-painted
> > > metal. I walked up to a white van parked in the sun. The chrome
> bumper was
> > > hot and the white body was cool. Hmmm.
> >
> > Hmmm indeed!. . . I clad an outbuilding on my shop lot with shiny
> > galvanized material and noted that in direct summer sun, the shiny
> metal
> > was so hot I could not bear to hold my hand on it while the white
> painted
> > metal next to it was very comfortable to touch . . . I expected the
> opposite
> > . . .
>
>
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