Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is color an intrisic property of a substance - even in a dark room?

  1. Feb 16, 2012 #1
    Is color an intrinsic property of a substance? I thought that if a red object is in an enclosed space, so that no light gets in, will no longer be red - and what makes the object "red" is that electrons absorb all colors of light and then reemit (reflect) the red light. Therefore, if no light reaches the object, it has no color - but I am probably wrong.
    This brings to mind another question or a possible conflicting scenario.
    A black object is a good absorber of radiation and an object that is white is a poor absorber of radiation. So, if I put a black coffee mug and a white coffee mug in a room that has no light, and the room is heated with infrared radiation, will the black mug absorb more thermal radiation? Does color ever come into play? Can someone please unravel my confusion?
  2. jcsd
  3. Feb 16, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    Color is a property that only exists inside our minds. Not in some sort of metaphysical sense or anything, but really. Each person sees colors a little differently. Different animals will perceive colors in a radically different way.

    Instead of color, one should talk about which wavelengths of light are reflected or absorbed. Wavelength is the same to everyone and isn't based on an individuals perception. Light with a wavelength of 450 nanometers will have that wavelength to ALL observers. In this thinking an object doesn't have a color because color doesn't exist. Intead it still has the same properties that it had before which is that it will reflect certain wavelengths of light. Whether there is or isn't light currently reflecting off the object matters not.

    The answer to your second question is complicated. While a black object may absorb more VISIBLE light than a white object, it doesn't mean that it absorbs other wavelengths better. It is entirely possible for a black object to completely reflect infrared radiation that a white object would absorb.
  4. Feb 16, 2012 #3


    User Avatar
    Science Advisor
    Gold Member

    Yes. Otherwise objects would change color depending on how bright a light you shine on them. What makes an object red is the molecular composition of its surface and how it absorbs and reflects different wavelengths of light. Just because an object is in the dark does not mean that its surface properties change.

    Yes, assuming the black mug is still black and the white mug is still white in the infrared spectrum. For example glass is transparent to visible light but strongly absorbs longer infrared wavelengths. Note that thermal radiation is light, just not in the visible spectrum at everyday temperatures.
  5. Feb 17, 2012 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Well said, the question should be presented in terms of the wavelength of light as opposed to the 'color' of something. The red we experience isn't a property of the light, it is something created by the brain. Birds for example have 4 cones in their eyes, so presumably, their perception of color is very different than ours.

    So to answer the question, no, color is not an intrinsic property of anything. The wavelength of light reflected or absorbed by something is the intrinsic property.
  6. Feb 17, 2012 #5
    Excellent and totally cool. I thank you for your clarification. I will now think of color as nothing more than EM waves with certain wavelengths. But drakkith brings up an interesting point when he said

    While a black object may absorb more VISIBLE light than a white object, it doesn't mean that it absorbs other wavelengths better

    I would think that an object that is a good absorber of all visible light (and would appear black) would also be a good absorber of all EM waves. (I'm guessing I am wrong on this as well). Isn't that what is meant by a blackbody - Which would be a pure black object that absorbs all EM waves?

    By the way, where do I find info on attaching quotes from responders?
    Last edited: Feb 17, 2012
  7. Feb 17, 2012 #6


    User Avatar
    Staff Emeritus
    Science Advisor

    A common household black trash-bag will absorb most visible light yet it is transparent to infrared light.
    To quote someone, you can click the "Quote" button at the bottom right of their post. To quote multiple posts click all the "Multi Quote" buttons and then hit "New Reply".
    If you want to quote part of a post you can use the Quote button inside the advanced reply. (The one you automatically go to if you hit New Reply instead of using the Quick Reply at the bottom)
    The button inside the advanced reply just puts
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook