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How much light does your average home mirror reflect?

  1. Sep 15, 2003 #1
    A few questions about mirrors:

    1) How much light (as a percentage) does your average home mirror reflect?
    2) How much light (as a percentage) does a very high quality mirror reflect?
    3) How much does a very high quality mirror cost?

    Last edited by a moderator: Feb 6, 2013
  2. jcsd
  3. Sep 15, 2003 #2
    I can speak a little for Astronomical use mirrors. They are front coated (the coating is placed on the front of the glass and you look at the coated surface) home type mirrors are back surface coated and you look through a layer of glass to see the reflected image, there is some distortion through the glass and light loss through diffraction, but the amount of distortion is minimal for everyday type use and the glass protects the coating.

    Optical grade mirrors are usually rated on the quality of the reflected image. A high grade Astronomical mirror for instance might be figured as a parabola, ground, polished and coated for 1/4 wave (fair), 1/8 wave (good), 1/10 wave (better), or diffraction limited (best).

    An 8" diameter, parabolic, 1/4 wave mirror can be had for about $70.00. A diffraction limited one of the same size might cost $400.00 or more (up to several thousand).

    Hope this helps some.
  4. Sep 15, 2003 #3


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    Re: Mirrors

    One time I scrounged some high-grade mirror from
    a university physics laboratory. They had cut something
    to size and had some odd-dimensioned scraps left over.
    No cost. Probably would have been thrown out.
    It was nice to handle (but hold it by the edges)
    and appeared to be extremely flat
    my memory of it is that the colors of things were
    deeper and less washed out than they appear
    in ordinary mirror but I cannot say for sure and
    I do not know the percentages.

    Edmond scientific catalog a natural place to look
    may be online now
  5. Sep 15, 2003 #4
    Re: Mirrors

    google will offer you better figures, but from memory, ordinary daily mirrors reflect as little as 40-60% of light. Lasers require 99.99% for full-reflection mirror and 99.9% for front escape mirror. They usually have such figures only in narrow band of wavelengths. Infact, upon eye inspection, laser mirrors are transparent to most except specific wavelengths.

    High quality wideband (relatively flat wavelength characteristic in visible light range) reflect 98-99.9%. Probably better figures too, but that'd cost exponentially more.

    Cost of very high quality mirror makes only sense when you tell your application. There's too many different things for different purposes. Obviously, size of mirror and surface precision has biggest impact on cost.

    If you live with prisms, then total internal reflection can offer 100% reflection in certain conditions.
  6. Sep 16, 2003 #5
    Also, if you are in the market for optical grade mirrors, try the surplus sources such as surplusshed.com An excellent source of inexpensive mirrors, lenses, etc.
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