The twisted nematic liquid crystal molecules of an LCD display are sandwiched between two sheets of glass with electrodes. Vertical and horizontal polarizing filters are positioned either side of this sandwich. The rod like twisted nematic liquid molecules are aligned to match the orientation of the vertical and horizontal filters on either side allowing light to pass through one filter, rotate and pass out the opposite filter.

The control electrodes are aligned in a matrix to provide an array of pixels consisting of three individually controlled sub-pixels with either a red, green or blue filter positioned in front. The level of voltage applied across the electrodes (and liquid crystal) is proportional to how much the naturally twisted liquid crystal will untwist and attenuate the light flow due to the difference in the polarizing filter orientations. A greyscale can thus be produced. The color gamut of each pixel is produced by the combination of color graduations from the color sub-pixels. The matrix of pixels for each display matches one of the standard resolutions (number of horizontal and vertical pixels).

Twisted Neumatic (TN) LCD displays are the most common however there are variations which have been designed to compensate for its limited viewing angles and limited color gamut.

• In-Plane Switching (IPS) has the two electrodes for each pixel on the same glass plate parallel to each other. This orientation offers no restriction to the angle at which light leaves a pixel improving the viewing angle and color reproduction in comparison to TN. Recent improvements in response times, contrast ratios and production costs have IPS displays poised for greater market penetration. Find out the details in our IPS vs TN LCD technology guide.
• Multi-Domain Vertical Alignment (MVA) has the liquid crystals that are perpendicular to the glass plates which have pyramid protrusions for liquid crystal rotation control. This approach gives wider viewing angles, a higher contrast ratio and faster response times. A major drawback is a reduction in brightness.
• Patterned Vertical Alignment (PVA) is a variation of MVA which gives higher contrast ratios.