Liquid Crystal Displays

LCDs use a fundamentally different technology from CRT displays. Instead of using a picture tube that fires electrons at the display, LCD technology uses special substances (the liquid crystals of the technology's name) that pass or block light to create different colors. The result is a display that's quite thin, as shown in Figure 14.2. Another advantage of LCDs is that they're completely flat.

Figure 14.2

The thinness and lightness of LCDs makes them ideal for use on notebook computers.

Figure 14.2

The thinness and lightness of LCDs makes them ideal for use on notebook computers.

Part III

Fundamentals of LCD Technology

Light can be thought of as a wave phenomenon, much like ripples in a pond. Any given light wave is oriented in a particular direction; for instance, horizontally or vertically. Ordinary light (from the Sun, a light bulb, or a candle, for instance) is composed of light waves of all orientations. Various substances, however, including certain crystals, can block light waves of a given range of orientations. The result is polarized light, in which all the light waves are oriented in the same way (see Figure 14.3). Humans perceive polarized light no differently from ordinary light, but the polarization allows additional manipulations of the light.

Figure 14.3

A polarizing substance passes only light of a certain orientation.

Figure 14.3

A polarizing substance passes only light of a certain orientation.

An LCD works by using two polarizing elements. The first polarizes the light, and the second can be adjusted electrically to pass—or not pass—this already polarized light. For instance, if one filter polarizes light horizontally, and if a second filter is also set for horizontal polarization, the light passes through. If the second filter is set for vertical polarization, on the other hand, 100% of the light is blocked.

Color LCDs use three cells for each pixel—one cell each for red, green, and blue. In this respect, color LCDs resemble color CRT displays, so other video hardware and software doesn't need to be modified to handle color LCDs. Like CRTs, LCDs use an additive color scheme.

Chapter 14

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