The TN display takes advantage of the ability of the nematic substance to rotate the polarization of light beams passing through it. Two polarizing filters, parallel planes of glass with their polarizing lines oriented at right angles with respect to each other, are positioned on either side of the liquid crystal. When light enters the display, it is polarized by the input filter. In the absence of an electric field, all the incoming light is transmitted. This is because the light polarization is rotated 90 degrees by the nematic liquid crystal, and the light therefore passes easily through the output filter, which is oriented to match the 90-degree shift.
With the application of a voltage , an electric field is produced in the nematic liquid crystal . Under these conditions the polarization effect is reduced. If the voltage is large enough, the polarization effect disappears altogether, and the light is blocked by the output polarizing filter.
Most TN displays have a characteristic black-on-gray or black-on-silver appearance, and are suitable for use in alphanumeric readouts such as those found in wristwatches, cell phone displays, and some calculator displays. The high-resolution LCD panels typically found in handheld and notebook computers use a different technology.