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 with out 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 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 to 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
> . . .
>
> Any physics major want to "splain" this to we with inquiring minds?
>
> Tony_Clark______________________lotus.tony@airmail.net
>
> >
> > Phil Ethier Saint Paul Minnesota USA
> > 1970 Lotus Europa, 1992 Saturn SL2, 1986 Chev Suburban
> > LOON, MAC
> > pethier@isd.net http://www.visi.com/mac/
> >
> >
> >
> >
> >
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