Black paint & radiant

jerry scharf_3

there is a physics concept of emmisivity. Something with 0 emissivityi s a perfect white body (mirror): nothing in, nothing out. The opposite is 1 emissivity, the perfect black body, everything in, everything out.

It turns out that flat white opaque paint isn't too different from flat black paint. Both have emissivity in the .85 to .9 range. Polished metals have very low emissivity.

jerry

singh

OK, we recently aquired a black lab pup, and I noticed how warm
his coat becomes when its sunny outside.

So it got me thinking about radiant and what effect darker color objects, and walls may have on overall comfort. I sure it will make no difference over long periods of time, but the waves will "see" dark first, right?

There has to be a study by someone out there, if not HR , break out that IR camera and buy some black paint, and let us know the results.

P.S. Our first lab, any tips from dog lovers.Maybe I should name him heat sink.

singh

That was the word I was looking for.

I remember the science class where we had an apparatus with two
flags inside a bulb,one black one white, on a sunny day they would spin.
the black flag absorbing the energy .

Jerry, why is paint almost the same and no effect,same in and out?

HeatJockey

paint colors

I remember an article by Dan (or found by Dan) discussing paint colors and metalic paint on radiators.

jerry scharf_3

a bit more

> That was the word I was looking for.

>

> I

> remember the science class where we had an

> apparatus with two flags inside a bulb,one black

> one white, on a sunny day they would spin. the

> black flag absorbing the energy .

>

> Jerry, why

> is paint almost the same and no effect,same in

> and out?




I remember the globe and paddles as well. They are converting light in the visible range to heat, and black paint is better at that.

What you need to rememebr is that the energy from the sun comes is many different frequencies/wavelengths that have different energies and characteristics. Many things reflect in one wavelength and absorb in another. Glass is a perfect example, where in the visible spectrum range (350-800nm) is transparent, but in the longer heat range (3000-40000nm) is opaque. That's what "greenhouse effect" is all about.

So in the visible light range the paints look very different. But in the heat range they turn out "looking" much different. It turns out that the pigments don't make so much difference in this range, and the base paint formulation makes more. So different levels of sheen and "covering ability" seem to be more important at this range.

When I want something I have a clue of for heat range emissivity, the folks at LBL did a spectral response of flat black rustoleum, and it's almost exactly at .9.

jerry

Jon_2

Black Lab puppies

Probably one of the nicest dogs you can have. Loves people, laid back (after he grows up) and a all around good friend. My favorite: English Springer Spaniel, they are real characters, love people so much they can drive you nuts at times, very active. It keeps me young watching and walking him. His antics will split your sides.

J.C.A._3

Sorry to get off subject.....

But I think he looks like either "Jake" or maybe "Boo". Looks like he could be a sneak up from behind and take care of things guy. Chris