# The interior of a Black car is not hotter than a White car



## Dave 330i (Jan 4, 2002)

I have often said that there is no difference in the interior temperature between a black and a white car after having been soaking in the hot sun all afternoon. Well, for saying that, I got a lot of ripe tomatoes thrown at me for not knowing what I was talking about. I think I do. I have experience on analyzing the thermal control systems of spacecrafts for many years. And, contrary what Mike 325xi said, I was not responsible for the destruction of Mars Observer during its orbital insertion into Mars.

My theory is that solar radiation (shortwave lengths) is the source of heating the interior of cars. Solar, mostly, ultraviolet rays, enter through the windshield and the windows. Once the heat enters, the windshield and the windows re-radiate the heat in the infrared regions, very similar to the heating coils baking your Mom’s cake inside her oven. Naturally, the metallic surface temperature of a black car is much hotter than a white car because black absorb more UV heat than white. But, we are comparing the interior temperature, not the exterior temperature.

Although my finding is not rigorously scientific, I believe that it has sufficient merit to show that the interior temperature of a black car is not substantially different from a white car.

Thermometers:
I bought two NSE instant read thermometers with a scale between 0 and 220 deg F. See picture. Since I could not tell whether they were accurate at room temperature, I selected two that had zero difference in temperature. Both read 78 deg at the time of purchase at Wal-Mart. My theory is that I want their offset to be zero at room temperature, and I am assuming that their offset is little or none at the steady state temperature inside the hot cars. I verified the offset at various temperatures, between 40F (inside the refrigerator) to inside my van at around 120 deg F. I was satisfied that there was virtually no difference in offset.

The Test
Houston had been relatively cool this summer, so I waited until today, Labor Day, to conduct my experiment. When I arrived at Advantage BMW in Clear Lake, the OBC of my 330i read 96 deg F (35.5 C). The time was 3:15 pm. I convinced a salesman to allow me to conduct my experiment. He introduced an E60 white 530i with tan leather seats, and an E60 black 545i with gray leather seat. I placed a thermometer on each driver’s seat and waited for about 15 minutes. The thermometers were not in direct sunlight as you can see. After 15 minutes, the salesman confirmed the temperatures with me. He was surprised that both thermometers showed 136 deg F (57.8 C). From this simple experiment I can conclude that this black car was not hotter than the white car when they were exposed to the sun most of the day in Houston. I am also convinced that the temperature rise inside of the car is caused mostly by infrared heating just like the inside of your oven where everything turns to the same temperature given time.

To non believers, go run the test anyway you see fit, and you will surprise yourself.


----------



## Alex Baumann (Dec 19, 2001)

LOL. Thanks Dave for taking time to set this up :thumbup:


----------



## SONET (Mar 1, 2002)

Nice job Dave! Interesting info.

BTW were the cars pointing the same direction?

--SONET

Edit: looking at the pics again it looks like they were parked right next to eachother, but still had to ask... :thumbup:


----------



## Dave 330i (Jan 4, 2002)

SONET said:


> Nice job Dave! Interesting info.
> 
> BTW were the cars pointing the same direction?
> 
> --SONET


No, that can be controverisal now. The windshield of the white car was in the sun. See the seat shadow of the white car (tan leather). But, I suggest that both cars have been sitting around all day, and at 3:15 pm, they probably reached its max temperature.


----------



## Mathew (Feb 8, 2002)

Way too many variables come into play here. First off, the cars are not in the exact same position. Also, you have to factor in the color of the seats, what type of options the cars have, whether or not the moonroof was exposed to the sun, build date, and mileage, not to mention the disparity in engine size.


----------



## Dave 330i (Jan 4, 2002)

Mathew said:


> Way too many variables come into play here. First off, the cars are not in the exact same position. Also, you have to factor in the color of the seats, what type of options the cars have, whether or not the moonroof was exposed to the sun, build date, and mileage, not to mention the disparity in engine size.


When I told you all those data you took was worthless you learned a lot from my judging your science projects at the CA Science Fair didn't you. :rofl:


----------



## TXE39 (Oct 2, 2003)

I think we can easily come to one conclusion:

When it's 96F outside in Houston it is going to be hot as hell in your car when you leave the store!


----------



## Rich_Jenkins (Jul 12, 2003)

Thanks for this info Dave, as the owner of a SG car with black interior in Fla I am glad I got black.

Now, where are those instructions for that rear sunshade...?


----------



## FenPhen (Jan 13, 2004)

Dave 330i said:


> I have often said that there is no difference in the interior temperature between a black and a white car after having been in the hot sun all afternoon.


I have no opinion about dark vs. light exteriors and interiors, but I also would have guessed the _temperature_ would be the same, but what about the feel?

A person's perception of heat is really perceived heat transfer, not the actual temperature. Dark-colored materials are very good at heat transfer, and light-colored materials are not (so black heats up quickly but also cools quickly). After both cars had been sitting for a long time, which seats feel hotter at first and which seats stay hot longer?


----------



## Dave 330i (Jan 4, 2002)

FenPhen said:


> I have no opinion about dark vs. light exteriors and interiors, but I also would have guessed the _temperature_ would be the same, but what about the feel?
> 
> A person's perception of heat is really perceived heat transfer, not the actual temperature. Dark-colored materials are very good at heat transfer, and light-colored materials are not (so black heats up quickly but also cools quickly). After both cars had been sitting for a long time, which seats feel hotter at first and which seats stay hot longer?


Heat transfer rate is not based on color but materials. You can not sense whether you sat on a black or tan leather seat. But, you can tell that you sat on steel because the heat transfer is greater. Just the same steel feels colder if the surface temperature is lower than your body's temperature. You can extend this reasoning to the cold feel of a tile vs. a wood floor in your house.


----------



## GregD (Feb 5, 2003)

I'm not surprised that the final steady state temperature would be the same in both cars after sitting out in the sun all day. I would be curious if there's a difference in how quickly they warm up.

Maybe something like this. On a hot day, use the A/C to get the temperature down to the mid 70s inside then stop, close the car up, and check the temperature every few minutes to see how long it takes to get back up to the steady state temperature. Then repeat for the other car.

Based on the cars I have had, I would expect the dark car to heat up more quickly than a light colored car. But I've never conducted a scientific experiment, so I'd be curious if someone tried the experiment I layed out above.


----------



## Mike 325xi (Dec 19, 2001)

Dave 330i said:


> And, contrary what Mike 325xi said, I was not responsible for the destruction of Mars Observer during its orbital insertion into Mars.


That's my story and I am sticking to it. 

I agree with GregD...I think a better experiment would be as to which car heated up faster in the exact same conditions. I'm not at all surprised that the inside temperature was the same after sitting all day but would like to see if they are the same in 15 minute increments as the day goes on.

Good experiment though. :thumbup:


----------



## ctbmw (Aug 30, 2003)

Sorry!
My black on black seems much warmer than my brothers silver on grey interior.
I also feel warmer wearing a navy shirt, than a white one.
Desert dwellers must feel the same way.
I then scanned your post again and attributed the diff. to an enclosed area. That made me wonder why solar panels are lined with black and not silver, or another color.
I still FEEL that a black interior is hotter. A look at all the Florida cars around here makes me think they're as clueless as me! Maybe it's because the darker colors fade quicker for some other reason than heat.


----------



## cruztopless (Sep 23, 2002)

I read an article about a year ago that talked about this very subject. Their finding was that cars are well insulated and the color of the car was not a factor on the car's interior temp. However, the color of the interior did make a difference.


:dunno:


----------



## Dave 330i (Jan 4, 2002)

ctbmw said:


> Sorry!
> My black on black seems much warmer than my brothers silver on grey interior.
> I also feel warmer wearing a navy shirt, than a white one.
> Desert dwellers must feel the same way.
> ...


Desert dwellers wear white because it reflects direct solar radiation. I mentioned that the exterior of a white car is cooler than a black car because black absorb more direct solar radiation. You are right in that the color of interior may make a difference. In the test I guess there is little difference in solar absorption after UV penetrates the glass between tan and gray leather seats. Since glass does not absorb all UV radiation, black surface is more In the car, infrared radiation is a greater contributing factor and the amount of UV actually going through the glass and absorbed by the seats may be negligible because the solar heat flux decays by an inversed square factor from the glass to the seat. So color of the seats may not be a big factor in determining the interior temperature. You can confirm this by placing your hand near and far from the glass, and you will notice the temperature difference by the inverse square law.

I plan to try other cars. I will make sure that the front of the cars are facing in the same direction.


----------



## ctbmw (Aug 30, 2003)

Dave 330i said:


> Desert dwellers wear white because it reflects direct solar radiation. I mentioned that the exterior of a white car is cooler than a black car because black absorb more direct solar radiation. You are right in that the color of interior may make a difference. In the test I guess there is little difference in solar absorption after UV penetrates the glass between tan and gray leather seats. Since glass does not absorb all UV radiation, black surface is more In the car, infrared radiation is a greater contributing factor and the amount of UV actually going through the glass and absorbed by the seats may be negligible because the solar heat flux decays by an inversed square factor from the glass to the seat. So color of the seats may not be a big factor in determining the interior temperature. You can confirm this by placing your hand near and far from the glass, and you will notice the temperature difference by the inverse square law.
> 
> I plan to try other cars. I will make sure that the front of the cars are facing in the same direction.


 You didn't really need to type all of that out did you?
Well you "dazzled" me. (world of difference between dazzled and convinced though).
(sorry)


----------



## Dave 330i (Jan 4, 2002)

ctbmw said:


> You didn't really need to type all of that out did you?
> Well you "dazzled" me. (world of difference between dazzled and convinced though).
> (sorry)


Learn more about heat transfer on a vehicle windshield... :rofl:

http://www.gmi.edu/~sroy/JTHT02.pdf

Another thing to consider...
Thermal capacity of leather holds more heat than fabric. It will also take it longer to get hot and longer to cool down. The rate at which it gains or loses heat from a hotter source or material to a cooler material (your butt) is controlled by how well you are insulated.


----------



## FireFly (May 2, 2002)

The experiment results do not surprise me at all. How can anyone believe that in a closed vehicle one color interior would be hotter than the other? The color has nothing to do with the heating process and heat retention.

I can guarantee you one thing: With a convertible you will notice a significant difference in the temperature of the seat when comparing two cars, tops down, sitting in the sun for hours. The black seats will be quite a bit hotter than a tan or light colored seat. You could not use the same thermo as used in the experiment above- you'd need to use a surface measuring thermo.

Great experiment though! I am sure many think black interior is/would be hotter.


----------



## LeucX3 (Dec 26, 2001)

Hmmmm, any science majors need a thesis idea?


----------



## ctbmw (Aug 30, 2003)

FireFly said:


> The experiment results do not surprise me at all. How can anyone believe that in a closed vehicle one color interior would be hotter than the other? The color has nothing to do with the heating process and heat retention.
> 
> I can guarantee you one thing: With a convertible you will notice a significant difference in the temperature of the seat when comparing two cars, tops down, sitting in the sun for hours. The black seats will be quite a bit hotter than a tan or light colored seat. You could not use the same thermo as used in the experiment above- you'd need to use a surface measuring thermo.
> 
> Great experiment though! I am sure many think black interior is/would be hotter.


 Results do not surprise, Yet convertible you will notice a significant difference.
I've been viewing this post too long.
It's late, I only know what I feel.
Once again-Sorry.


----------



## Dave 330i (Jan 4, 2002)

The temperature difference between a black and white car intrigues me. There are a lot of factors that come into heating the inside of cars. Developing the view factor model for an automobile is much more complicated than a spacecraft because a car has more materials, each with a different reflectance, absorptivity, and emissivity. You have radiation, convection, and conduction heat transfers. In addition, you have both UV flux, which becomes infrared flux, which are not constant heat fluxes. I plan to make more temperature measurements in the future so I can come to some postulations why a black car feels hotter than a white car.


----------



## Optimus Prime (Nov 11, 2003)

I couldn't read all the posts in this thread as my eyes started to roll up into the back of my head, but here are my $.02

1) The color of an object effects its radiant heat tranfer properties, the material effects it's conductive heat transfer properties.

2) The major driving force for exterior heating in a car is solar radiation through the windows. The color of the exterior of the car does have an effect, but it is minor.

3) Temperature and heat energy are different.

4) The color of the interior plays a larger roll than some think. A black interior will absorb more energy and release it faster. For that reason a Black interior can feel "hotter" than a light colored one of the same temperature.


----------



## Kaz (Dec 21, 2001)

I'm sorry, I'm having a hard time getting the image of Dave trying to convince a Texan car salesman to let him put thermometers in the cars. :lmao:

Aside from the various variables, this sounds like a sound experiment to me (OK, any way to reword that sentence?). But my white car with black interior is way cooler than my old black car with grey interior, so I'm with those who think there must be something else going on.

One thing I can attest to is that cloth definitely feels less hot than leather/ette in the same conditions. I distinctly remember sitting in italia330's car with black 'ette and feeling like I was burning my ass and back, then getting into my cloth seats sitting right next to it and being fine.


----------



## Dave 330i (Jan 4, 2002)

Kaz said:


> I'm sorry, I'm having a hard time getting the image of Dave trying to convince a Texan car salesman to let him put thermometers in the cars. :lmao:
> 
> Aside from the various variables, this sounds like a sound experiment to me (OK, any way to reword that sentence?). But my white car with black interior is way cooler than my old black car with grey interior, so I'm with those who think there must be something else going on.
> 
> One thing I can attest to is that cloth definitely feels less hot than leather/ette in the same conditions. I distinctly remember sitting in italia330's car with black 'ette and feeling like I was burning my ass and back, then getting into my cloth seats sitting right next to it and being fine.


Could it be because ette is a better conductor than cloth? If you touch steel at 175 deg your ass will get burned, but not with 175 deg ette. Your tile floor in your house feels colder to your feet than a wood floor. Are they at different temperature? To understand which is hotter or colder, you need to understand the material characteristics more than just whether it is black or white.

One thing I know, if you cover your car, the interior is heated by infrared from solar radiation on the cover. Everything inside comes to the same steady state temperature. Leather feels hotter because it is a better conductor than cloth. Whether the leather is black or white, it makes no difference. Two temperatures we are concern about, touch and ambient temperatures. In heating w/o direct solar radiation (cover on the car), the touch temperature and the ambient temperature are the same. With solar radiation, surface temperature is a fuction of the solar flux and the view factor between the windshield and the surface. Here are some temperatures I was able to obtain so far...

Deg F	Location	Direct Sun	Car Color/Make
136	tan leather seat	no	black BMW E60
136	gray leather seat	no	white BMW E60
120	floor gray carpet	no	dark green Ford Windstar
170	gray vinyl dash	yes	dark green Ford Windstar
130	gray cloth seat	no	dark green Ford Windstar
152	gray cloth seat	yes	dark green Ford Windstar


----------



## FenPhen (Jan 13, 2004)

hittinlike54 said:


> 4) The color of the interior plays a larger roll than some think. A black interior will absorb more energy and release it faster. For that reason a Black interior can feel "hotter" than a light colored one of the same temperature.


That's what I was offering, but reading through Dave's posts, I'm getting confused when color makes a difference and when it doesn't for car interiors.

All I know is that if you have a white cotton shirt and a black cotton shirt and both are sitting out in the sun, and then you put your hand on them, the black one feels hotter and cools faster (radiates heat?). If you're inside a black shirt versus a white shirt, you also feel hotter when in the sun. In the shade, there's no difference.


----------

