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If there were 2 rooms that were exactly the same except for colour would they have the same temperature? - Page 2

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Posted by BobVM on March 9, 2015, 6:54 am

A black surface is absorbing more radiation. A white surface is reflecting  
more radiation. If the black furniture is in the sun, it will be warmer.  
The white furniture will reflect solar gain. However, most of it will  
reflect it to somewhere else in the room. Some sunlight will be reflected  
out of the room, so the white furniture room might be slightly cooler. If  
it's summer on a sunny day, would you rather sit in a car with all black  
interior or a car with all white interior. The car with the black interior  
would be noticeably hotter, but much of the inside is black. It depends on  
how much black surface there is and if the sun is hitting it. The black  
surface may be absorbing over 95% while the white surface might only be  
absorbing 20-30% depending on the mix of white. Flooring receives a lot of  
sunlight, so if it's black they floor will be noticeably warmer. If it's  
white, then it will reflect more. It might go to another surface which  
might warm up instead. Over all, if a room was almost all white, a  
significant amount will reflect out of the room and it will be cooler. If  
you want one spot to be warmer, then color it dark. There will be a  
difference though not on a cloudy day or at night, only when significant  
solar gain is present. Also if the window area is small, then it won't be  
much different. If it's winter or cloudy, it might not be as much.

Posted by TomHR on March 23, 2015, 1:44 am
Hi BobVM,

 If it's winter or cloudy, it might not be as much.  

If the sun isn't shinning and it is cold outside, will the black room cool down faster?  If a dark color absorbs heat faster will it also resease it faster?

Posted by Morris Dovey on March 23, 2015, 11:32 am
 On 3/22/15 8:44 PM, TomHR wrote:

A black surface may appears black because it doesn’t radiate, reflect,  
or transmit energy at a frequency your eye can detect.

If you talk about energy flow to/from an object in terms of your own  
sensory apparatus, you’ll be missing just about all of it. ;-)

Morris Dovey

Posted by Morris Dovey on March 23, 2015, 11:45 am
 On 3/22/15 8:44 PM, TomHR wrote:

An object is “black” if it does not radiate, reflect, or transmit energy  
at a frequency/wavelength your eyeball can detect.

You might find some of the presentation at  
http://www.iedu.com/Solar/Energy/Absorber  interesting. :-)

Morris Dovey

Posted by Morris Dovey on March 25, 2015, 1:21 am
 On 3/22/15 8:44 PM, TomHR wrote:

That’s going to depend on the insulation, no?

Maybe yes, maybe no. However, the Stefan-Boltzmann law, states that the  
total energy emitted by a black body is proportional to the 4th power of  
its temperature...

You may want to read up on black/gray body radiation. See  
https://en.wikipedia.org/wiki/Black-body_radiation  and linked articles  
for a good starting point.

You’ll find there’s more to this than you’re probably expecting, and at  
first glance it looks intimidating – but the basic concepts are actually  
fairly simple (they’re just not particularly intuitive) :-)

Morris Dovey

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