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Thread: colors of the visible spectrum

  1. #1 colors of the visible spectrum 
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    I have another question about the visible spectrum. Can anybody please tell me which colors absorb the least heat and which colors absorb the most heat in order? Thanks


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    Forum Professor leohopkins's Avatar
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    Heat ?

    that is a tricky one.

    Okay.....black absorbs a lot of heat and white reflects it. Thats a fact we all know....

    Now, if someone knows better than I please do feel free to correct me on this, as it IS only a guess.

    But I would say that colours ( I think) absorb the same amount of heat (if the heat is being carried via radiation I.E Infra-red wave length.) because if somehting is green or blue or yellow, it is that colour because it is reflecting that particular wave length of light and absorbing all others (including infra-red) Obviously something that is infra red in colour doesnt absorb infra-red it radiates it, so if anything from both ends of the spectrum, you would have to have something shifting towards being the colour of infra-red to absorb heat less and less.


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    Forum Freshman wonkothesane's Avatar
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    I'm guessing also but I thought heat absorption would be a continuous function of wavelength and so red would absorb slightly more heat than blue. But I don't know, I'd like to, I hope somebody can tell us for certain.
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    Forum Senior anand_kapadia's Avatar
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    Quote Originally Posted by wonkothesane
    I'm guessing also but I thought heat absorption would be a continuous function of wavelength and so red would absorb slightly more heat than blue. But I don't know, I'd like to, I hope somebody can tell us for certain.
    or violet too
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    Forum Cosmic Wizard icewendigo's Avatar
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    Its not directly related but I think that the blue spectrum

    a) Blue light is an important part of the daylight's spectrum for our skin and some light related metabolic processes I think. Some time ago people found that Babies that had Jaunisse recovered better when exposed to sunlight, and now in hopitals babies with this problem are exposed to blue light (I dont know if its a specific type of blue light). Unless I am mistaking, by spending time in neon light instead of full spectrum sunlight we might be missing the needed blue spectrum.

    b) somehow penetrates deeper into water (or light is shifted to blue in water) while the red color is filtered out in deep water
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  7. #6  
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    In order to make this a little easier, let's re-phrase the question. Let's recognize, first of all, that "colors" do not "absorb heat". The fact that a black t-shirt appears to absorb more energy of the sunlight than a white t-shirt is not "caused" by the t-shirt's color. Au contraire, the absorption qualities of the particular fabric are causing the appearance of color to human eyes. Let's not confuse the direction of the causal relationship. I know that you guys all know that, but the language you choose to describe the phenomenon makes it easy or hard to "see the light", so let's be more precise with words.


    First of all we should define what's meant by "heat". A t-shirt you wear absorbs some of the energy that it receives from the sun via radiation. How is this felt as "heat" on your skin? There is something going on in the atoms of the fabric that transforms electromagnetic energy into the unorganized atomic motion that we perceive as heat sensation on our skins. What process is this, and how does it work? Why is this important to answer? Well, we know that high frequency waves (e.g. those associated with blue) carry more energy than low frequency waves (e.g. those associated with red), but does that mean the absorption of blue light results in more heat than the absorption of red light? Or could it be that some of the energy is reflected with frequencies outside the visible range?


    Then we need to think about what it means to absorb blue light or red light, respectively. The appearance of a t-shirt that absorbs light of all colors *except* red, will appear red to us. This would be a t-shirt that absorbs most of the high-frequency range of light. Likewise, a blue/violet t-shirt is an example of a shirt that absorbs mostly low-frequency light. Now, depending on the answer of the previous question, we will know which one actually heats up more. It might be as easy as answering the question: How much energy does the absorbed light contain?


    And that's still just part of the problem. Solar radiation consists of frequencies mostly within the light spectrum (that's why human eyes have evolved to see those particular frequencies), but there are fringes of infrared and quite a bit UV radiation. Infrared is directly perceived as heat, but what if this frequency were reflected by the outside surface of the t-shirt? Likwewise, are fabrics able to absorb UV radiation or do they reflect it? The answer to those questions might not directly have anything to do with the "color" of the t-shirt, but you should consider this: If a red t-shirt absorbs high-frequency waves such as those associated with blue, isn't it plausible that it also absorbs UV radiation? Likewise, does a blue t-shirt, which absorbs low frequencies, allow more infrared radiation to penetrate the fabric than a red t-shirt? And finally: Will UV radiation feel hotter than infrared, once transformed to heat, because it has a higher frequency (and energy)?


    There, I don't have definite answers to the questions, but at least I have the questions. :wink:
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    Forum Freshman Draculogenes's Avatar
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    You guys shouldn't do people's homework for them... tsk tsk
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    I don't mean to knit-pick M, but when you see something as being red, it means that its *complimentary* color was absorbed ( which for the color red is green). Each color in the visible spectrum has a complimentary color ( a wavelength that will cancel it out). so when something absorbs green, all the other colors of light are reflected to your eye, but all of them cancel out except red. It is a common misconception that everything but the color you see is absorbed. check out a good chemistry text book like Chemical Principles by Peter Atkins.
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  10. #9  
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    I don't mean to knit-pick M, but when you see something as being red, it means that its *complimentary* color was absorbed ( which for the color red is green). Each color in the visible spectrum has a complimentary color ( a wavelength that will cancel it out). so when something absorbs green, all the other colors of light are reflected to your eye, but all of them cancel out except red. It is a common misconception that everything but the color you see is absorbed. check out a good chemistry text book like Chemical Principles by Peter Atkins.
    Yes, that's the more general description. A t-shirt that absorbs all colors but green, will appear green. So does a t-shirt that absorbs only the complementary color magenta. The latter t-shirt will appear lighter (more light is reflected) than the first, and there is an infinite number of intermediate possibilities, resulting in shades of very radiant green to very dark green.
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