What voltage range is used to switch a typical twisted-nematic liquid crystal display?
In nematic arrangements the crystals are randomly positioned with all their long axes pointing in essentially the same direction, given by a vector known as the director. In smectic arrangements the crystals are further constrained to parallel planes; in smectic A the director is perpendicular to these planes, while in smectic C the director is at some other angle to the planes.
A typical twisted-nematic (TN) liquid crystal display is switched by applying a voltage range of three to five volts across the liquid crystal layer.1
When this voltage is applied, it destroys the twisted configuration of the liquid crystal molecules, causing them to orient themselves perpendicular to the substrate plates. This change in orientation alters the optical properties of the cell, resulting in a dark appearance. In the absence of voltage, the twisted configuration allows light to pass through the crossed polarizers, making the cell appear transparent.1