When a voltage is applied across the electrodes, a turning force oriented liquid crystal molecules parallel to the electric field, which distorts the helical structure (this can resist thanks to the elastic forces from the molecules are bound to surfaces .) This reduces the rotation of the polarization of the incident light, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules at the center of the layer are almost completely unwound and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light is mainly polarized perpendicular to the second filter, and so will be blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, the light can be allowed to pass through different amounts, constituting the different shades of gray.
LCD display alarm clock.
The optical effect of a device twisted nematic (TN) in the state of the voltage is much less dependent on variations in thickness of the device in the state of voltage compensation. Because of this, these devices are used between crossed polarizers so that appear bright without tension (the eye is more sensitive to variations in the dark state in the bright). These devices can operate in parallel polarizers, in which case the light and dark states are reversed.