What colour absorbs radiant heat more?

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Discussion Overview

The discussion centers around the absorption of radiant heat by different colored fabrics, specifically comparing a black t-shirt to a yellow one in the context of heat from an indoor gas heater. Participants explore the relationship between color, heat absorption, and emissivity, considering both visible and infrared wavelengths.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the difference in heat absorption between a black and yellow t-shirt is significant.
  • Another participant provides a link to external information, suggesting it may be useful for understanding the topic.
  • A participant explains that the color in the visible spectrum does not correlate well with infrared properties, noting that materials can behave differently in these wavelengths.
  • It is mentioned that while black shirts absorb sunlight well, they also radiate heat effectively, complicating the relationship between color and thermal properties.
  • Discussion includes the emissivity of cotton cloth in the infrared range, suggesting that color has little effect on thermal properties in practical scenarios.
  • One participant reflects on personal experiences with car colors and heat absorption, sharing anecdotal evidence of a white car being cooler than a dark red one, but acknowledges the lack of verification for the claims made by their father.

Areas of Agreement / Disagreement

Participants express differing views on the significance of color in heat absorption, with some suggesting minimal impact while others share anecdotal experiences that imply a more pronounced effect. The discussion remains unresolved regarding the extent to which color influences heat absorption in practical situations.

Contextual Notes

Participants note the complexity of the relationship between visible color and infrared absorption, highlighting the need for careful consideration of definitions and the specific conditions under which heat absorption is measured.

Dav333
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Hi.

In regards with a black vs yellow t-shirt, which absorbs radiant heat from a indoor gas heater more? Or is the difference too small to tell? Sorry I don't own a yellow tshirt.

thanks.
 
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The color of something is the visible waveband does not correlate well with it's 'color' in the infrared. Snow, for example, is black in the IR.

It can be a little tricky to figure out- the incident power from the sun peaks in the green/yellow (555 nm), but the peak wavelength corresponding to (say) 90 deg. F (32 C) is around 9.5 microns. So a black shirt will absorb sunlight very well, but may also radiate the heat very well.

For a gas heater, most of the radiant energy is around (IIRC) 3-5 microns. Again, the color in the visible has little to do with the optical properties in this waveband.

As it happens, cotton cloth has an IR emissivity (8-12 microns) of about 0.8

http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=Emissivity.htm&ID=254

Close to the absorptivity in the visible. I couldn't find values for the mid-wave IR.

What that means, in practice, is that the color of the fabric has very little effect on the thermal properties.
 
Andy Resnick said:
The color of something is the visible waveband does not correlate well with it's 'color' in the infrared. Snow, for example, is black in the IR.

It can be a little tricky to figure out- the incident power from the sun peaks in the green/yellow (555 nm), but the peak wavelength corresponding to (say) 90 deg. F (32 C) is around 9.5 microns. So a black shirt will absorb sunlight very well, but may also radiate the heat very well.

For a gas heater, most of the radiant energy is around (IIRC) 3-5 microns. Again, the color in the visible has little to do with the optical properties in this waveband.

As it happens, cotton cloth has an IR emissivity (8-12 microns) of about 0.8

http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=Emissivity.htm&ID=254

Close to the absorptivity in the visible. I couldn't find values for the mid-wave IR.

What that means, in practice, is that the color of the fabric has very little effect on the thermal properties.

Awesome, very informative, thanks.
 
I always kind of assumed it was true that light colors reflected heat and dark colors absorbed heat, but I didn't really think about it. I have a white car that gets pretty hot sitting in the sun. Does it get just as hot as a black car? My dad has a dark red van and measured the heat on the paint to be pretty hot. He painted it white and measured it to be cooler than it was when it was dark red. I didn't see it and can't verify if it was conclusive. I'm just taking his word for it.
 

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