Appearence of objects which do not reflect light

  1. On Facebook recently one of my friends asked the question 'What would a mirror look like if it did not reflect light?'. To this my immediate response was along the lines of:

    > An object which reflects no light but absorbs all light will be the darkest and most opaque object imaginable
    > An object which reflects no light but transmits all light will be completely and utterly invisible

    But then I got thinking... what would an object look like which reflects no light, absorbs some light and transmits the rest? Based on the conclusions above common sense tells me that the object could be described as translucent grey/black although I am far from convinced by this conclusion.

    So here are my questions: was my initial response correct? What would an object which reflects no light, absorbs some light and transmits the rest look like? Does such an object exist?
  2. jcsd
  3. Sounds like a tinted window. But that does reflect a little light.
  4. QuantumPion

    QuantumPion 883
    Science Advisor
    Gold Member

    How about the sky?
  5. What you are describing is similar to a camera filter or good sunglasses (ones that don't change the colour). They also tend to reflect some light but reflections can be reduced by using special surface coatings. Typically you will see objects on the other side of the material but they won't appear as bright as some light bounced off the objects is absorbed. The material may appear "translucent grey/black" in comparison with transparent air around it. It's a fair description.

    The absorbed light will raise the temperature of the material which might cause it to increase emissions in the infra red part of the spectrum but you can't normally see that unless you use an infra red camera to convert the infra red back to visible light.

    Aside: If you make a pair of sunglasses from this material your eyes might compensate for the reduced brightness by increasing the size of your iris and that would effect your depth of focus. So objects seen through it might not all be in focus anymore.

    PS: If the refractive index is different to air then objects may appear distorted or out or position.
  6. My first choice also.

    If one didn't know any better, or feel the wind and see leaves and trees moving about because of, or of suspended matter such as clouds, fog and dust within, it is as if there is nothing. Transmission of light is nearly 100%.

    We see reflections of light that makes it back to our eyes, from objects a distance away, such as in the daytime, or from the light of the moon, streetlights, or flashlights. At night time, and no mass is in the way, we see the light emmitted or reflected by objects in a really far distance and we call them stars, comets, planets.

    Windows do the same thing. They take on the appearance of the objects on the other side of the window from us, or turn black at night. Of course, there is some reflection also, and we usually do not notice it.
  7. Matterwave

    Matterwave 3,865
    Science Advisor
    Gold Member

    An object which absorbs all light but does not reflect light is a black body. It will heat up and glow. If it's not hot enough, it might indeed appear black since it might glow mostly in the infrared.

    A mirror which does not reflect light is not a mirror.
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