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as 60 Hz, but the terms mean slightly different things between the two technologies. With CRTs, as you’ll recall, the phosphors on the screen start to lose their glow and need to be hit again by the electron guns many times per second to achieve an unwavering or flicker-free image. Each dot on an active matrix LCD, in contrast, has its own transistor to light it up. There’s no need to freshen up the dot; it’s on or off. Regardless of the refresh rate for the LCD, therefore, there’s never any flicker at all.

The refresh rate for an LCD monitor refers to how often a screen can change or update completely. Think of the refresh rate as a metronome or timer and you’ll be closer to how it works in an LCD. For most computing issues, 60 Hz is fine and that’s been the standard for the industry. Humans see things that change as infrequently as 24 times per second—the standard for motion pictures at the cinema, for example, and the best high-definition (HD) signal—as a full motion video. To be able to change almost three times faster is perfectly acceptable, even in higher-end applications such as fast-moving games.

Monitor manufacturers have released 120-Hz LCD monitors in a response to the convergence of LCDs, televisions, and computers to enable you to see HD movies or standard-definition (SD) content without any problems or visual artifacts on an LCD monitor. The easiest number that provides a whole-number division for both 24 frames per second and 30 frames per second was 120 Hz. The latter is the standard for SD content.

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NOTE A video card needs to be able to support Dual-Link DVI to run a 120-Hz monitor or television. See the discussion on DVI later in this chapter for details.

Contrast Ratio

A big drawback of LCD monitors is that they don’t have nearly the color saturation or richness of contrast of a good CRT monitor—although LCD technology continues to improve every year. A good contrast ratio—the difference between the darkest and lightest spots that the monitor can display—is 450:1, although a quick trip to a computer store will reveal LCDs with lower levels (250:1) and higher levels (1000:1).

LCD monitor manufacturers market a dynamic contrast ratio number for their monitors, which measures the difference between a full-on, all-white screen, full-off, or all-black screen. This yields a much higher number than the standard contrast ratio. My Samsung panels have a 1000:1 contrast ratio, for example, but a 20,000:1 dynamic contrast ratio. Sounds awesome, right? In general, the dynamic contrast ratio doesn’t affect viewing on computer monitors. Focus on the standard contrast ratio when making decisions on LCD screens.

Projectors

Projectors are a third option for displaying your computer images and the best choice when displaying to an audience or in a classroom. There are two ways to project an image on a screen: rear-view and front-view. As the name would suggest, a rear-view projector (Figure 19-24) shoots an image onto a screen from the rear. Rear-view projectors are always self-enclosed and very popular for televisions, but are virtually unheard of in the PC world.

A front-view projector shoots the image out the front and counts on you to put a screen in front at the proper distance. Front-view projectors connected to PCs running Microsoft PowerPoint have been the cornerstone of every meeting almost everywhere for at least the past ten years (Figure 19-25). This section deals exclusively with front-view projectors that connect to PCs.

Figure 19-24 Rear-view projector (photo courtesy of Samsung)

Figure 19-25 Front-view projector (photo courtesy of Dell Inc.)

Projector Technologies

Projectors that connect to PCs have been in existence for almost as long as PCs themselves. Given all that time, a number of technologies have been used in projectors. The first generation of projectors used CRTs. Each color used a separate CRT that projected the image onto a screen (Figure 19-26). CRT projectors create beautiful images but are expensive, large, and very heavy, and have for the most