A thinking puzzle for Nimo

Giganews Newsgroups
Subject: A thinking puzzle for Nimo
Posted by:  George Johnson (matrix…@charter.net)
Date: Wed, 26 Nov 2008

I have a cubic block of 27 glass cubes.

    All of the glass cubes are glued with clear glue into the shape of one
big glass multi-part cube.
    All of the glass cubes on the outside of the big multi-part cube are
transparently tinted (about 25%) red.

    The middle cube is either clear glass or also tinted red also.

    Using only light (flashlights of any color and lasers of any color are
allowed) and a light meter, can you tell me if the middle cube is clear
glass or red-tinted glass?

    You are not allowed to unglue, unstick, break apart, damage, melt,
fracture, or separate the individual glass cubes or dissolve the clear glue.
    All of the glass cubes weigh identically to each other (although their
weight is unimportant)/

    The cube wall is shaped like this on each side:

    No prizes are rewarded for answering this question.
    No punishments will be given.
    This question is exclusively for Nimo to answer how, using light and
metering devices alone as a means to obtaining an answer.  Refraction is a
clue as is beam interference for an easy cheat (although the glue would make
that cheat difficult).  Neither is necessary to obtain the obvious answer.

    This will lead somewhere in the field of data compression later, but for
now I want Nimo to do some pondering and not presenting of random ideas
without basic testing.