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Polaroid Glasses and TI Calculators
Name: trumpetman
Status: N/a
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993
Question:
When looking at a TI graphing calculator with an LCD display while
wearing 3D or Polaroid sunglasses, quite interesting colors result depending
on the orientation of the filters in the glasses. Why does this occur?
Replies:
The colors result from a correlation between the wavelength of
light that makes it through the LCD and the polarization of that light. I do
not know the details of an LCD, but I can describe a similar, and simpler,
effect that you might be interested in. Take two Polaroid filters (Polaroid
sunglasses are fine) and place a crinkled up piece of cellophane between them.
You will see beautiful colors that vary with the orientation of the filters
and with the thickness (number of layers) of cellophane between them. This
effect is easier to discuss because we are in complete control of the
polarization of incoming light. We start with a definite polarization of the
light that makes it through the first Polaroid--the polarization is
independent of wavelength. Then, the cellophane *rotates* the plane of
polarization of light passing through it; the amount by which the polarization
is rotated depends on the wavelength. These two things happen because the
index of refraction of cellophane depends both on the wavelength and on the
polarization of the light passing through it. The second Polaroid accepts
only light with a particular polarization, so, if "yellow" got its
polarization rotated by the right amount to make it through both Polaroids,
"blue" will probably not have. If you want to know more, you might look for
information on the term "birefringence". Although I know little about LCD's,
I strongly suspect a very similar thing is going on there.
Mooney
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Update: June 2012
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