CA May Ban Black Cars

I disagree in many respects. The insulating effect of the average car's headliner is minimal at best. If the upper surface is upwards of +20deg on a dark car then some of that heat is going to be radiated off the metal body into the interior up to the point at which the temperature of the interior rises above that of the metal of the car and then we may see a reverse effect but I bet the windows or other items will serve as the eventual outlet for that added heat as they are likely cooler than the body. Would there be an inside temperature difference between 2 metal sheds if one was painted white and the other black and neither of them had any windows?

I do agree that short wave radiation coming in through the windows does heat up the interior and that a darker colored interior will absorb more of that radiation and cause the interior to heat up more than a light-colored interior, no one is arguing that.

This is similar to the reason why people paint their roof white. A white roof has a higher albedo and can help to conduct excess heat out of the interior once the interior is hotter than the roof or body panels. It can start this process at a lower interior temperature than it would if you had a dark car that was approx. +20degrees higher than a white car.

Here is more information on white roof tops. Some of this can be transfered to autos as well.

White Roofs Cool the World, Offset CO2, and Delay Global Warming


As a side note. The more I think about this the more it seems like the temperature gain would eventually stabilize and that the interior temperature may be similar in a white car vs. a black car and the only large variation would be how quickly one car's interior heated up vs. the other. Hmm now I don't know what to think.

 

We didn't measure the inside temps at all. This was quite some time ago and since I am no longer in the car club I'm not sure when I'll get another chance to test so many identical cars with different colors in the same place at the same time. lol

Sadly, the thermo-gun is normally used to measure the track surface temp and tire temps before and after a burnout. God I was a bad kid!

 

How about some formulae to settle this. Wasn't it Max Planck who defined black body radiation?

And what about the possibility of a causal relation between human albedo and libido? I think more research is needed.

 

Ohh here we go..... The Planck Constant gets applied to EVERYTHING!

Libido can indeed heat up a car's interior but it is moist heat and not dry heat. There is a difference! Just ask someone from Florida or ask your cars windows after prom......

 

Boring

Not boring

 

Albedo and libido seem to be inversely related. So far, I think Jamaicans are the hottest.

 

It has been many years since I was doing fugitive emissions calcs for storage vessels, but the color of the vessel was a recognized factor in the calcs from what I recall.

 

No, because the hotter roof will result in a higher equilibrium temp. inside. The magnitude of the driving forces change with roof temp, so a new equilibrium will be achieved with a different heat gain via the roof. And a hotter roof means an incrementally hotter interior temp, all else being equal.

Whatever sort of other heating or cooling is occurring, the system will eventually come into some sort of balance (assuming enough time passes with the same input conditions.) So if you increase or decrease one of the inputs, it will shift the equilibrium.

This sort of issue comes up in amateur astronomy at times. Darker tubes radiate heat away more rapidly than the more scientific looking white tubes. However, the wavelengths of concern at night are much longer (infrared) than in the day, so the "real" effective color difference of the paint is much less. With telescope optics it is important to reach equilibrium as soon as possible to reduce tube currents. (Tube currents will really foul up an image.) I typically set my scope up pointed at the sky for an hour or so before I begin observing.

With a telescope one faces two major problems with this radiative cooling. First, you want your main (heavy) optics to cool to a point where they are close to equilibrium with the nightsky or you get some severe astigmatic appearing tube current effects off of the primary mirror. Remember radiative heat transfer is an absolute temp to the 4th power function, and that a clear, dry night sky is incredibly cold. This produces the second problem, if the dew point is not really low, then your optics tend to begin dewing or frosting (at least at 5 F I have trouble with the eyepieces developing frost if I don't carefully exhale out the corner of my mouth high and above the eyepiece) after a few hours. Ironically, with a Newtonian scope, it is the secondary mirror that dews first--but some nichrome wire can be used on it to keep it from dewing since it does not suffer much wavefront distortion at this point.