Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: mcjhn on 13/02/2011 15:34:19
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someone told me that a material's colour does not effect its IR absorption/emission properties.
if so wouldn't wearing white result in you absorbing less visible light and being cooler?
or am I missing the point and its because white cloth is more expensive/not fashionable or do people mostly stay indoors during the daytime or something else?
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It has to do with insulation and circulation. White clothes let the radiation through, black absorbs it. If you have loose fitting clothes the black will create convection between the layer of cloth and your skin. The warm air will raise, finding its way out to become replaced by cooler air, so in a way it's a natural air-conditioning. But the clothes have to be 'baggy' and loose fitting for this to work.
You see a lot of white animals in arctic climates.
"With even a modest wind (anything above 3 m/s, or about 7 m.p.h.) fluffed white plumage exhibit the lowest net heat loss. This explains the large number of arctic animals that are fluffy and white. It's not just camouflage.
At high temperatures, as I say, white is best at not transmitting solar/ambient heat to the skin when windspeed is zero (only barely better when fluffed). However, with an increase in windspeed (again anything above 3 m/s), fluffed black plumage is the best at reducing the amount of heat transmitted to the skin. Flattened black plumage is the worst in terms of heat gain no matter what the windspeed."
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Well. White wool is transparent. Is white cotton transparent?
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It's just a generalized description Sim. All fabrics will be transparent if thin enough, but black materials less than white, due to the way they can absorb and transform the visible radiation to heat.
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It's just a generalized description Sim. All fabrics will be transparent if thin enough, but black materials less than white, due to the way they can absorb and transform the visible radiation to heat.
Then white thick cotton is better than black thick cotton.
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Isn't it more of a fashion statement than anything else?
"Oh how gauche! Didn't you read Vogue dear? This year it's all about black."
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It's just a generalized description Sim. All fabrics will be transparent if thin enough, but black materials less than white, due to the way they can absorb and transform the visible radiation to heat.
Then white thick cotton is better than black thick cotton.
Not if you want the convection, then black should be what you aim for. White reflects light of all wavelengths whilst a red cloth absorbs all other colors than red better, how good it absorbs those other will be seen as how 'red' the cloth will be to you, also depending on the light-source of course. Black also reflects all colors, just like white, but as it absorbs so much of them the net effect becomes a 'black'. That I didn't mention it before was because I was trying to keep to what the main question was 'why do people wear black in the desert.'
But you're right, it bears on the question under the caption. It also have to do with the type of eyes we have. They don't separate by wavelength only, they're not built on that principle it seems. Our brain take the information received from the eyes which it then interpret. That's the reason why yellow can be seen both with the frequency reflected being 'yellow' around 580 nm, (http://en.wikipedia.org/wiki/Color) or be perceived as being the same with a equal blend of red and green, both saying 'yellow' to us.
"The retina contains three types of color receptor cells, or cones. One type, relatively distinct from the other two, is most responsive to light that we perceive as violet, with wavelengths around 420 nm; cones of this type are sometimes called short-wavelength cones, S cones, or blue cones.
The other two types are closely related genetically and chemically. One of them, sometimes called long-wavelength cones, L cones, or red cones, is most sensitive to light we perceive as greenish yellow, with wavelengths around 564 nm; the other type, known as middle-wavelength cones, M cones, or green cones is most sensitive to light perceived as green, with wavelengths around 534 nm.
Light, no matter how complex its composition of wavelengths, is reduced to three color components by the eye. For each location in the visual field, the three types of cones yield three signals based on the extent to which each is stimulated. These amounts of stimulation are sometimes called tristimulus values.."
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Black is the most improper color of clothes and especially of footwears in a solar summer(in Volgograd).I know it. [;)]