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Why do darker colors absorb heat/light?

  1. Mar 30, 2003 #1
    Why do darker colors absorb heat/light?
    Last edited by a moderator: Feb 4, 2013
  2. jcsd
  3. Mar 30, 2003 #2
    Re: colors

    The question needs minor re-phrasing. You see, the fact that something is a certain color is caused by it's absorbing certain wave-lengths of light (not the other way around).
  4. Mar 30, 2003 #3


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    More minor clarification: The color is caused by BOTH what is absorbed and what is reflected (for opaque objects).

    So the question is self-answering.
  5. Mar 31, 2003 #4

    Another God

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    Now that the question has been re-phrased, perhaps someone would like to answer it?

    Oh, OK....i'll do it....

    What they mean Majin, is that our experience of colour occurs because only particular light wavelengths of the spectrum are reflected. The wavelengths which are reflected are what we see, and the wavelengths which are absorbed are the colours we do not see.

    So a green leaf, is actually absorbing all of the colours which are not green (to oversimplify...)

    As for colours absorbing heat. I ahve never heard that as such. Colours = Light though, and light = energy, and energy = heat... maybe there is some sort of connection there.
  6. Mar 31, 2003 #5
    Have you ever seen a "reverse radiometer"? (At least I think that's what it's called.) I saw it on the deleted scene of "The Time Machine". It looked a lot like a wind-mill, but moved by the energy of the sun, as opposed to the energy of wind. You see, it's fins were colored white on one side, and black on the other side, and thus only one side of each fin was absorbing the sun-light, while the other side reflected it. This translated to kinetic energy, and the "reverse radiometer" began to spin.
  7. Mar 31, 2003 #6


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    Yeah, the connection is the one you made. By the commutative property of math, light = heat (more or less). Every color corresponds to a specific temperature.
    You mean you DIDN'T have one in your high school pysics lab? Wtf?!!
  8. Mar 31, 2003 #7
    If you hold up a vial of chlorophyl dissolved in alcohol, its reflected light (light behind you) appears green, but its transmitted light (light behind vial) appears red! The differences between frequencies times Planck's constant must be close to the reaction energy of ATP<-->ADP?
  9. Mar 31, 2003 #8
    Most radiometers are not sensitive enough to turn primarily by photon momentum transfer. Rather, the black and white sides of the fins heat up differentially the rarified gas present within the radiometer and cause motion with the white side leading. Photons, I think, would cause rotation in the opposite direction. Not an efficient way to generate large amounts of energy here on Earth.
  10. Apr 2, 2003 #9
    ermz ..so why do leaves absord all the other colours except for green?
  11. Apr 2, 2003 #10
    Actually, that's not correct. The reaction centers in chloroplasts absorb two photons, at 680 and 720 nanometers. This is used to reduce water, shunt protons across a membrane, and reduce NADP+. The protons go on to produce ATP, and the NADPH drives the Kreb's cycle, which produces sugars, which can be oxidized to produce ATP. But it's a far, far way from being a 100% effecient system.
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