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LCDs Versus Plasmas

Jun 1, 2003 12:00 PM, Peter H. Putman, CTS


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The past year was significant for the flat-screen display industry in more ways than one. You saw increasing use of the digital video interface, as well as numerous rounds of price cuts and more aftermarket support for video scaler cards.

But the most significant news was that the 30-inch barrier for single-fabrication LCDs was finally shattered — and then some. Sharp, LG Philips, and Samsung all showed LCD monitors and TVs with screen sizes ranging from 32 inches to 54 inches throughout the fall and at CES 2003.

You probably spotted a few of those displays at NAB, NSCA, and InfoComm. If so you might be wondering how those new monitors will affect the plasma market and whether you ought to be specifying thin-film transistors (TFT) LCD monitors for an upcoming job instead.

For now most of these large LCD monitors are still in the prototype stage, though Sharp is shipping a 37-inch integrated wide-screen TV for the home, and Samsung has a new 40-inch wide-screen model for industrial and consumer use. The 46-, 52-, and 54-inch sets seen at CES are probably a year away from mass distribution.

However, that's not so far down the road, and chances are you'll see even larger TFT LCD monitors announced later this year — right up to 60 inches. A quick glance at the offerings of plasma manufacturers and resellers shows show that Samsung's 63-inch plasma display panel (PDP) is the largest available, but it could be eclipsed in the not-too-distant future by LCD technology.

LCD: ODDS-ON FAVORITE?

Not surprisingly, many of the companies that are major players in plasma also have ambitious LCD manufacturing efforts underway. Samsung and LG are upgrading their fabrication lines to get to 60 inches and above in the next year. NEC has a partnership with Mitsubishi to make LCDs and is showing a 40-inch prototype wide-screen display, which will no doubt have a model number by the time you read this.

Although Sharp doesn't manufacture plasmas, it sells more LCD TVs than anyone in the world and is heavily invested in LCD technology, with a new manufacturing facility scheduled to come online in the next two years. It will be able to roll out panels as large as 60 inches with high pixel density.

Plasma has a price advantage over LCD. But that's because of an oversupply of plasma product and too much manufacturing capacity. One industry veteran recently characterized LCD technology as “costing three times as much as plasma but lasting three times as long.”

Does either technology really have the upper hand? Will one eventually win out? My guess is it will be LCD imaging, but there are a host of reasons why.

To start with, plasma imaging works pretty much the same way as a fluorescent light. A high-voltage discharge across a small cell gap ionizes an argon-neon gas mixture within the cell, and the resultant burst of UV light causes phosphors in each cell to glow. This characteristic of emissive imaging is similar to that of a cathode-ray tube, which stimulates phosphors to glow with a high-voltage electron beam.

Because the voltages used are high (usually, 150V or more to create the initial discharge and 75V or more to sustain the pixel), plasma monitors get quite warm. They also use a lot of electricity, with a typical 50-inch panel consuming between 450W and 500W. The discharge also results in an audible buzz, which until recent years was difficult to muffle.

Plasma's biggest problem is burn-in. Depending on how hard the display is driven, bright parts of a static image may permanently burn into the color phosphors. You can easily spot this phenomenon anywhere that plasma monitors are used for public display, such as in an airline terminal. Unless care is taken in setting the contrast (picture) to a reasonable level, burn-in will occur rapidly and is almost impossible to remove.

The second problem with plasma is burn-out. All those rapid discharge/sustain/erase cycles put stress on the phosphors. Over time their ability to respond diminishes to the point in which the panel's full brightness is reduced by about 50 percent. At this point, the panel is generally considered to have reached the end of its useful life.

How long does it take to burn out? No one knows for sure. Many factors contribute to the problem. Guesses for plasma life range between 10,000 and 20,000 hours. My guess is that a panel should last between 10,000 and 15,000 hours, provided it's set up correctly for reasonable brightness levels.

LCD monitors suffer no such problem. Granted, the individual pixels can become stuck if any of the TFTs fail. But that's not as much of a problem as it was a decade ago. What will eventually burn out is the fluorescent backlight, for much the same reasons as plasma. The gas discharged through the backlight tube will eventually cause the backlight phosphors to drop to about 50 percent of their original brightness.

At this point, the backlight is considered exhausted. But it can be replaced separately from the LCD panel. The only question is, would anyone bother to do so, given the depreciated value of the panel after 40,000 to 60,000 hours? That's what Sharp and other companies claim for backlight life.

To put that number into perspective, if you watched 4 hours of TV a day for a year, that would total about 1,450 hours. Assuming you could get 45,000 hours from the LCD monitor's backlight, it should last you about 30 years. Even if the backlight reached half brightness after 30,000 hours, that's still a 20-year duty cycle.

For public display, assume a 16-hour duty cycle with 7-day operation and a 2-week maintenance shutdown. That's 112 hours a week, or 5,600 hours per year. Assuming 40,000 hours as the half-life figure, your LCD monitor should run about seven years before it's ready for the scrap heap. That's well outside a reasonable depreciation window.

AND THEN THERE WAS LIGHT

Plasma has an edge over LCD in that it's an emissive display. When you view a plasma screen, you're looking right at the source of light energy — the color phosphors. As a result, plasma monitors have excellent contrast, excellent (though not necessarily accurate) color saturation and fidelity, and wide viewing angles, just like a direct-view monitor or TV.

LCDs, in contrast, are light shutters. The liquid crystal molecules in each pixel align themselves in response to changing voltages to block or pass polarized light, based on the principle of birefringence. That makes it difficult to get lots of light out of LCD monitors, and it also cuts down on the effective viewing angles, just like a rear-projection TV.

But steps are also being taken to solve those problems. Sharp, Samsung, and LG Philips all have developed new vertical alignment modes for LC molecules. You'll hear these modes called Advanced Super View, Patterned Vertical Alignment, and Super In-Plane Switching, respectively, and they all improve viewing angles, contrast, black levels, and brightness.

SATURATION

Another advantage that plasma has over LCD is the level of color saturation you can get with phosphors as compared with the micro color filters applied to each liquid crystal pixel. The pictures from some of the best PDPs can look every bit as good as a CRT image, and it will be a while before LCD color filter technology gets to that level.

But LCDs trump plasma in their pixel density. As a rule, LCD pixels have a much smaller pitch than those of PDPs. As a result, it's possible to have 22-inch to 46-inch LCD monitors and TVs with true high-definition pixel counts (1,280 by 768 to 1,366 by 768), and the new 52-inch and 54-inch LCD monitors shown by LG and Samsung actually have 1,920-by-1,080-pixel physical resolution. It will be some time yet before plasma monitors can achieve that kind of density.

The third reason that LCD technology will eventually win out has to do with how it is controlled. Switching of TFT pixels is done with a silicon back plane, as opposed to the grid of electrodes used in a plasma panel. The manufacturing facility for those back planes can just as easily spit out 15-inch and 22-inch LCD TVs as it can the bigger models.

Organic light-emitting diodes (OLEDS), an emerging technology that will hit its stride later in this decade, also use a TFT back plane to switch them on and off. With bright, emissive colors and low operating voltages, OLEDS will eventually push plasma out of the market. A factory that makes TFT back planes can service either of the two technologies.

GOING TFT

The talk is that TFT LCD technology will take over the smaller multimedia screen markets up to 42 inches in the near future. Evidence suggests that the price gap between plasma and LCD is already narrowing. Forty-two-inch plasma monitors with 1,024-by-768 nonsquare pixel arrays (made by NEC, Panasonic, and Pioneer) sell for about as much as Sharp's new 37-inch LCD monitor that has 1,366-by-768 pixels and just a little less than Samsung's new 40-inch 1,280-by-768 LCD offering.

At CEDIA Expo in September, check to see how many companies are adding LCD TVs and monitors to their product lines. You may be surprised to see all the players, and you'd be even more surprised if you knew where each reseller's LCD glass originated. There are a lot of odd-couple partnerships being formed to get flat-screen displays into the marketplace, and they are mostly driven by overcapacity and the need to establish a toehold in the lucrative North American market.

When it comes to flat-screen technology, most of the resellers and OEMs are completely agnostic. All they care about is the screen size and an attractive price, and when TFT LCD monitor manufacturers can deliver both in quantity, you'll see a gradual movement away from plasma.


Peter H. Putman owns PHP Communications, in Doylestown, Pennsylvania. The author of The Toastmasters Guide to Audio/Visual Presentations, Putman is also a regular columnist in S&VC.



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