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White and silver

  1. Mar 13, 2008 #1
    What's the difference between white and silver color? If both the sufaces are reflecting all the light frequencies, why do they look different?
     
  2. jcsd
  3. Mar 13, 2008 #2

    Danger

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    I really have no knowledge of optics. My uneducated guess would be that it has to do with the angles at which the light is reflected.
     
  4. Mar 13, 2008 #3
    A polished metal, like a mirror, will reflect a ray in one particular direction. Angle of incidence equals angle of reflection. That's called mirror reflection or specular reflection. If you eye isn't at that special angle then you won't see the ray. But that's no good for a movie screen. You want the movie screen to reflect rays in all random directions, so some of them will hit everyone's eye. That's called diffuse reflection. So we paint a movie screen white.
     
  5. Mar 13, 2008 #4

    rbj

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    actually, i think that professional movie screens (as well as modern home theater front projection screens) have very tiny reflective beads (perhaps called "micro lenses" in the patent) that are silvered and round. i'm having trouble finding technical info, but take a look at the previous patent citations in this patent.
     
    Last edited: Mar 13, 2008
  6. Mar 14, 2008 #5
    Silver isn't really just a color; it also has a characteristic shine which distinguishes it from white. This is because of free electrons in the metallic surfaces. These free electrons, unlike the bound electrons in atoms, can resonate at any frequency and can, thus, emit light at all frequencies (thus the similarity to white, which is a combination of all visible frequencies). As I understand it, light hitting silver doesn't go very far into the material because of the high cross sections for electron interaction, thus producing a metallic luster on the surface.
     
    Last edited: Mar 14, 2008
  7. Mar 14, 2008 #6
    To avoid the angle of incidence/reflection factors,. let's take the case of a perfectly spherical shaped silver object. Shouldn't silver color closer to perfect white (by the definition of white color) color, than the traditional white color, bacause it absorbs the lesser of the incident light?
     
  8. Mar 14, 2008 #7
    A silver sphere would be a convex mirror (with a lot of spherical aberration). It wouldn't look white. You would see a small upright reflection of yourself.

    Silver spheres are used as Christmas tree decorations. Looking at a little piece of a convex mirror, like the security mirror in a store, or the "objects in mirror are closer than they appear" sideview mirror of a car, reveals generally what a perfect sphere would do. Looking at a very imperfect replica, such as the outer side of a shiny spoon, reveals generally what a perfect sphere would do.

    Buy you could never see your reflected image on a white surface no matter how purely white it is. At every point on the white surface you would would see a superposition of every source of light in the environment, all scattered everywhere.
     
  9. Mar 14, 2008 #8

    rcgldr

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    You can have a very glossy white surface that is reflective, for example, a mirror with a hint of white or any other color, but the color results from partial (or nearly full) conversion of the received light into light of a specific color.
     
    Last edited: Mar 14, 2008
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