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LCD ABCs
Dual Scan (Passive Matrix)
Active Matrix
Resolution
LCD measurement
Technical support
Video definitions

LCD ABCs

An LCD, or Liquid Crystal Display, is the display used with all portable computers today as well as is beginning to be used with flat panel monitors and higher end computers. The LCD is made of two sheets of a flexible polarizing material with a layer of liquid crystal solution between the two.

The LCD does not refresh like a standard computer monitor utilizing the CRT method of refreshing the image. Instead, the display is created by sending various voltages of electricity to cells of liquid crystal causing the liquid crystal to untwist at the rate of electricity applied, generating 64 different shades per cell.

DUAL SCAN (PASSIVE MATRIX)

A dual scan display, which is sometimes referred to as a passive matrix display, has a row of transistors running on the top of the screen (x-axes) as well as the left of the screen (y-axes). The amount of transistors are defined by the LCD manufacturer, for example, the manufacturer may define 800 transistors along the x-axes and 600 transistors along the y-axes. These transistors power the pixels that are powered in grids by the transistors. Unfortunately, if one of these transistors were to fail, you would receive a solid black line going vertical or horizontal.

When compared to an Active Matrix, most Passive Matrix is superior technology. With Passive matrix you are unable to see the screen unless you are directly in front of it. Generally, the display is going to be dimmer than a Passive Matrix.

New Passive Matrix screen technologies, such as CSTN, or Color Super-Twisted Nematic, DSTN, or Double Layer Super-Twist Nematic, and HPA, or High-Performance Addressing displays, are improved versions of the Passive Matrix displays which improve upon previous versions by offering higher contrast / brightness rates found with earlier versions.

In conclusion, the Passive Matrix today, while better than previous versions, is still an affordable solution as an LCD display. However, it does not offer the quality that is found with Active Matrix.

ACTIVE MATRIX

Unlike Dual Scan, Active Matrix has transistors for each pixel, generating their own light, creating a more brighter and crisp display. Because of this method used for display, the screen can also be viewed by multiple viewers.

While the Active Matrix does have a crisp display because each pixel has its own transistor, you will find that power will drain more quickly than a dual scan display. In addition to the power being consumed more quickly than a Dual Scan because of the amount of transistors, there is more of a chance for dead pixels.

In conclusion, the Active Matrix may have disadvantages like any technology; however, it is generally a recommended technology over the Dual Scan technology.

Unlike the resolution on a computer monitor, the LCD has a fixed amount of liquid crystal cells and can only display one set resolution defined by the LCD manufacturer.

Because of this, an LCD screen which has a set resolution of 1024 x 768 can have a smaller display, however when the screen is decreased in size it will not use the complete screen causing the image to have a black border around image. Most new computers will have a capability of stretching this image causing the image to utilize the full screen but this degrades the display, especially noticeable on text.

LCD MEASUREMENT

The size of a computer monitor is determined by going from the bottom left corner to the top right corner. However, if you have a 17" monitor, the viewable area may only be e 14.5" to 15"

However, when measuring LCD panels, there is no loss of display. Generally, you will see laptop manufacturers rating the LCD in various sizes, these sizes and what they are comparable to are listed below.