liquid crystal display

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liquid crystal display

[′lik·wəd ′krist·əl di′splā]
A digital display that consists of two sheets of glass separated by a sealed-in, normally transparent, liquid crystal material; the outer surface of each glass sheet has a transparent conductive coating such as tin oxide or indium oxide, with the viewing-side coating etched into character-forming segments that have leads going to the edges of the display; a voltage applied between front and back electrode coatings disrupts the orderly arrangement of the molecules, darkening the liquid enough to form visible characters even though no light is generated. Abbreviated LCD.

liquid crystal display

(LCD) An electro-optical device used to display digits, characters or images, commonly used in digital watches, calculators, and portable computers.

The heart of the liquid crystal display is a piece of liquid crystal material placed between a pair of transparent electrodes. The liquid crystal changes the phase of the light passing through it and this phase change can be controlled by the voltage applied between the electrodes. If such a unit is placed between a pair of plane polariser plates then light can pass through it only if the correct voltage is applied. Liquid crystal displays are formed by integrating a number of such cells, or more usually, by using a single liquid crystal plate and a pattern of electrodes.

The simplest kind of liquid crystal displays, those used in digital watches and calculators, contain a common electrode plane covering one side and a pattern of electrodes on the other. These electrodes can be individually controlled to produce the appropriate display. Computer displays, however, require far too many pixels (typically between 50,000 and several millions) to make this scheme, in particular its wiring, feasible. The electrodes are therefore replaced by a number of row electrodes on one side and column electrodes on the other. By applying voltage to one row and several columns the pixels at the intersections are set.

The pixels being set one row after the other, in passive matrix displays the number of rows is limited by the ratio of the setting and fading times. In the setup described above (known as "twisted nematic") the number of rows is limited to about 20. Using an alternative "supertwisted nematic" setup VGA quality displays (480 rows) can be easily built. As of 1995 most notebook computers used this technique.

Fading can be slowed by putting an active element, such as a transistor, on the top of each pixel. This "remembers" the setting of that pixel. These active matrix displays are of much better quality (as good as CRTs) but are much more expensive than the passive matrix displays.

LCDs are slimmer, lighter and consume less power than the previous dominant display type, the cathode ray tube, hence their importance for portable computers.


(Liquid Crystal Display) A screen display technology developed in 1963 at the David Sarnoff Research Center in Princeton, NJ. All computer and most TV screens are LCDs (see LED TV), while mobile device screens may be LCD or organic LED (see OLED). By the 1990s, color LCDs helped laptop sales boom, and LCD computer monitors outsold CRTs for the first time in 2003. See liquid crystal, LCD types and LCD categories.

A Color Pixel
Sandwiched between polarizing filters and glass panels, rod-shaped molecules of liquid crystals flow like liquid and bend light like crystal. The liquid crystal layer is 5 to 25 micrometers thick (2 to 10/10,000" inch). For more details on color LCDs, see LCD subpixels.

Seven-Segment LCD Watch
Because it took so little power to move crystal molecules, LCD wristwatches and other monochrome screens began to flourish in the late 1970s. For more details on this type of display, see seven-segment display. (Image courtesy of the private collection of Peter Wenzig.)

LCDs and LEDs are widely used in combination as in this printer panel. Readouts are LCDs, but the indicator lights on billions of products are LEDs. LCD TVs use LED backlights (see LED and LED TV). See LCD vs. OLED and LCD vs. plasma.
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