Twisted nematic (TN) technology for LCDs
Light and dark
TN flat screens are constructed from multiple layers. The ultra-thin layer of liquid crystal mixture, twisted by 90°, is located between two thin panels of glass coated with clear electrodes. Polarization filters are found on the outside of the glass plates, while on the inside there are color filters, transparent electrodes, and a two-sided layer for orienting the LC molecules. The thin layer of liquid crystals, around four to eight micrometers thick, is the heart of every LC display. In conjunction with polarization filters, it works as a "light valve" for the backlight. The first polarization filter allows only a specific oscillation level of light to pass through. The light then meets the liquid crystals. When voltage is applied, the molecules align themselves perpendicular to the glass plates.
The light follows this alignment, but is unable to pass through the second polarization filter, which is rotated by 90°. The result: the pixel becomes dark. If no voltage is applied, the molecules fall back into their original twisted arrangement. The light follows this rotation and is thus able to cross the second filter, too: the pixel becomes light. Because almost no electricity flows through the LCD, this type of display is extremely energy efficient.
The TN cell was invented around 1971 by James Fergason, Martin Schadt, and Wolfgang Helfrich.