The backlight of an LCD isn't itself polarized. A TN LCD display is made of two orthogonal polarization filters with the liquid crystals in between. In their re

The backlight of an LCD isn't itself polarized. A TN LCD display is made of two orthogonal polarization filters with the liquid crystals in between. In their relaxed (twisted) state, the crystals rotate the polarization of the light so that it can pass the second filter. When a voltage is applied, the crystals straighten and the second filter blocks the light.