liquid-crystal display: Definition and Much More from Answers.com

LCD
(Liquid Crystal Display)A display technology that uses rod-shaped molecules (liquid crystals)that flow like liquid and bend light. Unenergized, the crystals directlight through two polarizing filters, allowing a natural backgroundcolor to show. When energized, they redirect the light to be absorbedin one of the polarizers, causing the dark appearance of crossedpolarizers to show. The more the molecules are twisted, the better thecontrast and viewing angle.
Because it takes less power to movemolecules than to energize a light-emitting device, LCDs replaced thelight-emitting diodes (LEDs) in digital watches in the 1970s. LCDs werethen widely used for a myriad of monochrome displays and still are. Inthe 1990s, color LCD screens caused sales of laptop computers toexplode, and in 2003, more LCD monitors were sold for desktop computersthan CRTs.
The LCD was developed in 1963 at RCA‘s Sarnoff Research Center in Princeton, NJ. Seeflat panel display,LCoS andindium.
TYPES OF LCDs
Passive Display (TN, STN)
Called "passive matrix" when used for computer screens and "passivedisplay" when used for small readouts, all the active electronics(transistors) are outside of the display screen. Passive displays haveimproved immensely, but do not provide a wide viewing angle, andsubmarining is generally noticeable. Following are the types of passivedisplays.
TN - Twisted Nematic - 90º twist
Low-cost displays for consumer products and instruments. Black on gray/silver background.
STN - Supertwisted Nematic- 180-270º twist
Used extensively on earlier laptops for mono and color displays. DSTNand FSTN provide improvements over straight STN (180º - green/blue onyellow background; 270º - blue on white/blue background).
Dual Scan STN
Improves STN display by dividing the screen into two halves andscanning each half simultaneously, doubling the number of linesrefreshed. Not as sharp as active matrix.
Active Display (TFT)
Widely used for all LCD applications today (laptop and desktopcomputers, TVs, etc.). Known as "active matrix" displays, a transistoris used to control each subpixel on the screen. For example, a 1024x768color screen requires 2,359,296 transistors; one for each red, greenand blue subpixel (dot). Active matrix provides a sharp, clear imagewith good contrast and eliminates submarining. Fabrication costs wereoriginally higher than passive matrix, which caused both types to beused in the early days of laptop flat panels. Active matrix displaysuse a 90º (TN) twist. Also called "thin film transistor LCD" (TFT LCD).Seedead pixel.
Reflective Vs. Backlit
Reflective screens used in many consumer appliances and handhelddevices require external light and only work well in a bright room orwith a desk lamp. Backlit and sidelit screens have their own lightsource and work well in dim lighting. Note that the meaning of"reflective" in this case differs from light reflecting off the frontof the screen into the viewer‘s eyes. Seetransmissive LCD for a comparison.
 

Twisted-Nematic Seven-Segment Display
Seven separate segments are used to make up the digits 0 through 9. In this illustration, the center segment is used as an example. The unenergized segment (left) causes the crystals to line up with the front and rear polarizers. The segment appears light gray, which is actually the light traveling down and reflected back up the crystals.
The energized segment (right) causes the crystals to become perpendicular to the polarizers. The segment appears dark, which is the effect of crossed polarizers. Most LCDs use a translucent reflector with light behind it, which makes the background brighter and the characters sharper. (Redrawn from illustration courtesy of LXD, Inc.)
 

Seven-Segment LCD Watch
This was one of the first seven-segment LCD watches on the market in the early 1970s. Notice how digits are made up from the seven different segments. (Image courtesy of the private collection of Peter Wenzig.)
 
 

 

LCD Vs. Plasma
LCD and plasma displays use entirely different means to create colors. LCD uses liquid crystals and color filters while plasma uses gas and phosphors (see plasma display).
 

LCD Vs. LED
LCDs and light emitting diodes (LEDs) are widely used in combination as in this printer control panel. Alphanumeric readouts can be LCD or LED, but the billions of on/off indicators found on countless products such as this green Ready light are LEDs.