Using cellophane to convert a liquid crystal display screen into a three dimensional display



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3. Manipulating polarized light


Polarized light is used not only because our eyes are insensitive to the polarization of the light wave, but also because its path can be selectively blocked or transmitted by using a polarizer. If the polarizer's transmission axis is parallel to the polarization direction of the incident light, the light passes through the polarizer with minimum attenuation. On the other hand, if they are perpendicular to each other, the light is absorbed by the polarizer and does not transmit through.

Now, we can take advantage of the fact that the light emanating from the liquid crystal screen of a laptop computer or a camera phone is linearly polarized2. The light from the liquid crystal display is linearly polarized simply because the top surface of the liquid crystal screen is covered by a polarizer sheet as one of the necessary parts of the liquid crystal display.



In Fig. 2, a triangular-shaped polarizer sheet is held up to a laptop computer screen.





(a)

(b)

The transmission axis of the polarizer is perpendicular to the direction of polarization of light from the screen.

The polarizer in (a) is rotated by 90°. The transmission axis of the polarizer is now parallel to the direction of polarization of light from the screen.

Fig. 2 A triangular-shaped polarizer sheet is held up to a laptop computer screen.




In Fig. 2(a), the polarizer sheet is oriented with its transmission axis perpendicular to the polarization direction of the light from the screen. With this orientation, the polarizer sheet is quite effective at blocking the light from the screen. In Fig. 2(b), the transmission axis of the polarizer sheet is rotated by 90 so that it becomes parallel to the polarization direction of light from the laptop screen. With this orientation, the polarizer sheet becomes transparent. The same type of demonstration can be made using the screen of a camera phone.
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