The distinctions stem from the fundamentally different methods the technologies use to produce images. LCD monitors operate by shining light through a thin-film transistor layer and using filters to produce specific colors. Plasma screens zap neon gases trapped inside a pixel matrix to create ultraviolet light, which, in turn, excites red, green, and blue phosphors.
These descriptions are simplistic, but they shed light on the pros and cons of the two options. Indeed, LCD makers face a serious challenge with backlighting because of the difficulty of evenly defusing light over larger panels. As a result, despite the enormous popularity of LCD monitors for the desktop, LCD panels still can't match the physical size of the larger plasma displays. In fact, any LCD panel that measures 24 inches or more diagonally is classified as large, and the largest thus far measures just over 40 inches. By comparison, plasma displays generally range in size from 40 to 62 inches, with the largest reaching 76 inches.
However, plasma display manufacturers face different obstacles. For example, it's been difficult for them to squeeze the gas mixtures into ever smaller pixel grids. The resulting shortcoming in resolutions, VGA at best, is one reason why there are so few plasma panels on the market less than 40 inches (a 32-inch model is the smallest). What's more, reducing the overall size of the pixel matrix does not dramatically lower the cost, which makes smaller plasmas impractical from a price perspective.
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For video professionals, that's too bad, because plasma screens do a better job than LCDs of producing vibrant and accurate colors. With plasma monitors, the viewer is looking directly at the light and color source, and the higher video quality is apparent in side-by-side comparisons. Also, the responsiveness of phosphors enables plasma displays to avoid the motion refresh and ghosting problems associated with LCDs. And a smaller distance between pixels on plasma screens creates a more natural appearance.
LCD panels, on the other hand, do a better job in higher ambient light environments than plasma or CRTs because they don't reflect as much light. Thus, LCD panels ultimately are finding increasing success in video production environments. For example, while many LCD monitors may not appeal to color-correction experts or high-detail producers, they have proven invaluable where space is tight, as in production trucks and control rooms. The technology also uses less power than CRTs and plasmas, which can be an advantage on location. In any case, the bottom line is that while LCD video quality is not up to the level of plasmas or CRTs, it is now good enough for all but the most demanding applications.
LCD panels also outshine plasma displays in video applications where burn-in might be a problem, as is the case with constantly visible time-coding or logos. Fortunately, with the constantly changing images of motion video, plasmas tend to burn in more evenly and less overtly. Yet longevity is still a potentially critical shortcoming of plasma monitors. At best, phosphors age and create a loss of contrast over time. At worst, burn-in leaves permanently ghosted graphics or text.
Further, LCD monitors support much higher resolutions than plasma, up to 1920x1200 in high-performance models. Therefore, they tend to have a crisper, sharper appearance. Plasmas can't match that resolution because of the physical space required for the pixel grid and, therefore, rarely exceed Wide XGA resolution. The exception is alternate lighting of surface panels (AliS), which claim higher horizontal resolution but light only half of it at a time.
So is it simple enough to say that plasmas are good for video and LCDs are good as computer monitors? Perhaps. Odds are that if plasmas could become small enough, those rack-mounted panels of video production monitors might well be plasmas. Perhaps we'd also see plasmas on airplanes and in the backseats of minivans. But, that's not likely. For those uses, LCD solves specific problems, and because of the R&D dollars being invested in LCD, the technology is improving rapidly. And the popularity of LCD-TV products from companies such as LG Electronics, Samsung, Sharp, Sony, and ViewSonic suggests LCD is advancing in video applications.
Plasma monitors that are 40 inches and larger currently have a quality and price advantage for video applications. Although a similarly sized LCD would offer higher resolution, it might cost 50 to 100 percent more. Given that, plasma may be the better choice for large-panel video applications for at least the next few years.
Still, LCD makers enjoy the huge economies of scale from volume laptop and desktop monitor sales that may ultimately overwhelm plasma. For instance, LCD makers are now working with promising new ways to backlight panels, such as with LEDs, that may dramatically increase the color range and brightness uniformity of LCDs. In contrast, the plasma maker's biggest R&D hurdle is eliminating burn-in, which is likely to take many years to overcome.
In professional video production applications—for which LCD has reached high-enough levels of image quality and fast-enough refresh rates—users are already finding that space-saving is more important than the drop-off in image quality. When bigger is better for video, 40 inches and above, plasma is still the choice. That may change, but the competition will mean that LCD quality should continue to improve as well and make "thin" an even more capable solution for professional video editing and graphics.
Jeff Sauer is a contributing editor of Computer Graphics World
and director of the Digital Video Group, an independent research and testing organization for digital media. He can be reached at jeff@dtvgroup.com.