LIQUID CRYSTAL DISPLAY

Liquid Crystal Display (LCD) is a flat-panel display technology that is used in most laptop computers. LCD technology can also be used for other display devices, such as car radio displays, clocks, desktop computers, and any other display devices that can take advantage of flat-panel technology. The biggest advantages of LCD flat screens are that they reduce physical space requirements, they are lightweight and portable, and they require less energy to operate. (Laptop LCDs are powered by low-voltage DC.) Traditional CRTs take up more desktop space than LCDs and require more energy to operate. With an LCD display, what you see is basically what you get. Unlike CRTs, in which the nominal size is less than the described measurement of the monitor, the measurement of an LCD screen is accurate. In other words, if you purchase a 15-inch LCD, you get a 15-inch display. LCD monitors are now available in all sizes, from 15 inches through 23 inches. Please note that while LCD monitors are great space savers, they are far more expensive that standard (and even flat-panel) CRT monitors.

LCD technology uses two panels of a polarizing substance, with a liquid crystal solution between the two panels. An electric charge is sent through the crystals, causing them to form a shield from light. The crystals either allow or disallow the passage of light, and eventually form an image.

Different types of LCDs serve different purposes and provide various levels of display quality. Some of the more common types are as follows.

Passive matrix LCD: A passive matrix display uses LCD elements, electrical current, and a grid of wires to control the passage of light. It has a fixed resolution of pixels.

Active matrix LCD: This LCD type is based on Thin Film Transistor (TFT) technology. It constantly refreshes each pixel, providing a consistently sharp image. This technology provides better visual quality than passive matrix and is more expensive.

Dual scan: With dual scan, the LCD screen is divided in two. Each half of the screen is refreshed separately. This process increases the resolution rate, but decreases the brightness (contrast) level of the LCD.

Monitor Power Management

A monitor uses a tremendous amount of AC. The Environmental Protection Agency (EPA) came up with a program and a set of standards, known as Energy Star™, to reduce the amount of energy used by monitors and PC-related equipment. To see if a monitor is Energy Star compliant, click Start > Settings > Control Panel > Display > Screen Saver. If the monitor is compliant, you will see the Energy Star logo and “Energy saving features of monitor” (Figure 19.3).

Figure 19.3: Windows Energy Star Compliance logo.

Important Monitor/Video-related Information and Test Tips

The following important monitor/video-related information and test tips are included to give you an extra boost in the exam room. Pay close attention here; this information may help you in the field as well:

Using a video resolution of 800x600 is equivalent to using SVGA video mode.

Video cards are most often designed for AGP slots.

If your monitor goes blank after changing your video resolution from say 640x480 (16 Colors) to 800x600, (16-bit high color) it is likely that your refresh rate has been set too fast for your monitor to handle.

The amount of time required for CRT’s electron beam to draw or “paint” a screen is called refresh rate.

4MB of video random access memory (VRAM) would be required to display 1024x768 at 24-bit color.

If you have a monitor that is displaying abnormal odd colors such as green or orange, there is a high probability that your monitor is either defective or you have a bad or bent pin on your monitor’s cable connector.

WRAM is used for and on many video cards today.

If you find yourself browsing the Internet and you can’t see entire pages displayed on your monitor, the first thing you should do is adjust your video resolution settings.

Always unplug the power from your system when installing video cards.

In order for a system’s POST (Power-On Self-Test) to complete at boot up, it must recognize video support.

If you change your monitor’s refresh rate and nothing will display on your monitor, the first step you should take is to restart the computer and enter Safe Mode. Safe Mode will load the basic video drivers and setting, which will further allow you to troubleshoot.

A VGA connector has 15 pins.

If a signal to an Energy Star Compliant monitor does not vary or change, it can change or “switch” to a lower power status.