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 Click here to return to the Physics Archives

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