# What radiates more heat, white or black?

#### ShawnD

If I have 2 objects that are the same is every way except for the color, which object will radiate heat faster; the black or the white?

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Black.

#### Artman

FZ is right as the question is worded. However, it depends on if the surrounding space is warmer or colder. If it's warmer it will be absorbing heat faster.

#### jimmy p

Gold Member
well i have never heard of white body radiation...

#### Integral

Staff Emeritus
Gold Member
It really is not that easy of a question to answer. Color is not specifically a factor in any thermodynamics relationship. What is a factor is surface emissivity. If the bodies are the same in every way the temperature of the 2 bodies will only be different the emissivity has changed. (This may well happen)

#### russ_watters

Mentor
Originally posted by Artman
FZ is right as the question is worded. However, it depends on if the surrounding space is warmer or colder. If it's warmer it will be absorbing heat faster.
Faster than what? The question wasn't whether it would absorb or emit, but which would emit more: Black. The way the equations work, you can consider an object to be simultaneously absorbing and emitting radiation.

#### ShawnD

Ok now is there a reason for why black emits more? I mean like a real reason not just a vague logical explanation.

#### Integral

Staff Emeritus
Gold Member
Black tends to adsorp a wider band of energy then lighter colors which reflect more, thus black surfaces can be warmer then light. There is much more then just color involved, so this is pretty much a generaliztion which may not be true in every case.

#### Artman

Originally posted by russ_watters
...The question wasn't whether it would absorb or emit, but which would emit more: Black. The way the equations work, you can consider an object to be simultaneously absorbing and emitting radiation.
He also said radiate HEAT faster. If the space around them is colder than the two objects, which will radiate heat faster? The energy emitted may not be in the form of heat.

#### ShawnD

Actually the surroundings make no difference. Let's say you have 2 objects, one of them black and one of them not black and both are gaining more heat than they are emiting. The black object will radiate more heat as well as absorb more heat.

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