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Plasma versus LCD

PLASMA vs LCD TV

Review Date 6-3-2004
By Phil Conner

This is a complicated topic: when you're choosing between plasma and LCD TVs, you're actually choosing between two competing technologies, both of which achieve similar things (i.e., crystal-clear, color-filled pictures) and come in similar packages (i.e., super-model-thin cases). To complicate the decision-making process further, price is rapidly becoming a non-issue here.


Despite all these similarities, these technologies differ as to how they process and display incoming video/computer signals.

Plasma technology consists hundreds of thousands of individual pixel cells, which allow electric pulses (stemming from electrodes) to excite rare natural gases-usually xenon and neon-causing them to glow and, thus, produce light. This light illuminates the proper balance of red, green, or blue phosphors contained in each cell to display the proper color sequence from the light. Each pixel cell is essentially an individual microscopic florescent light bulb, receiving instruction from software contained on the back electrostatic silicon board.

Whether spread across a flat-panel screen or placed in the heart of a projector, all LCDs are pretty much the same. A matrix of thin-film transistors (TFTs) supplies voltage to liquid-crystal-filled cells sandwiched between two sheets of glass. When hit with an electrical charge, the crystals untwist to an exact degree to filter white light generated by a lamp behind the screen (for flat-panel TVs) or one shining through a small LCD chip (for projection TVs). LCD monitors reproduce colors through a process of subtraction: They block out particular color wavelengths from the spectrum of white light until they're left with just the right color. And, it's the intensity of light permitted to pass through this liquid-crystal matrix that enables LCD televisions to display images chock-full of colors-or gradations of them.

PICTURE CONSIDERATIONS:

CONTRAST

Plasma technology has certainly achieved quite high contrast ratios. Panasonic has even boasted that its plasma displays have a 3000:1 contrast ratio, which is the measure of the blackest black compared to the whitest white. Plasma displays achieve such impressive black levels by using internal algorithms to block the power to particular pixels in order to render a pixel "dark" or black. While this can limit a plasma's gray scaling, it does produce exceptionally black blacks.

LCD (liquid crystal diode) displays, by contrast, utilize electric charges to untwist liquid crystals, which causes them to block light and, hence, emit blacks. The higher the voltage passing through the liquid crystals in a given pixel, the more fully those crystals untwist and effectively block light-all of which makes these pixels darker. This is a complicated process. And, despite recent improvements in LCD black levels, even the best LCD displays (like those produced by Sharp) have yet to break the 1000:1 contrast-ratio barrier. Though, at 700:1, many of the best quality LCD panels display sufficiently dark blacks to please even the most discriminating eyes.

Advantage: Plasma. For scenes with a lot of dark and light images shown simultaneously-as with content originating from DVDs, video games, and NTSC TV signals-plasma TVs will consistently outperform LCD TVs.

plasma tv compared verglijken met lcd vs
COLOR SATURATION

In plasma displays, each pixel contains red, green, and blue elements, which work in conjunction to create 16.77 million colors. Insofar as each pixel contains all the elements needed to produce every color in the spectrum, color information is more accurately reproduced with plasma technology than it is with other display technologies. Not only are the chromaticity coordinates more accurate on most plasma displays, the color saturation resulting from the pixel design of plasma displays is remarkable.

LCD displays reproduce colors by manipulating light waves and subtracting colors from white light. This is an inherently difficult template for maintaining color accuracy and vibrancy-though most LCD displays manage quite well. While color information benefits from the higher-than-average number of pixels per square inch found in LCD displays (especially when compared to plasmas), LCDs are simply not as impressive as plasmas with similar pixel counts.

Advantage: Plasma, with the following caveat: While plasma displays are especially good for moving images, LCD technology is better at displaying static images with particular crispness and even coloration.

VIEWING ANGLE

Plasma manufacturers have made much of their 160° viewing angles, which is about as good as horizontal and vertical viewing angles get. This owes to the fact that each pixel is lit by itself, not from some central light source. Hence, each pixel is more readily visible because its brightness is consistent with every other pixel on the screen.

LCD manufacturers have done much to improve their displays' viewing angles. The substrate material on newer-generation LCDs by Sharp and NEC has helped to expand those units' viewing angles, though they have a long way to go before catching up with those on plasma units. Expect the best LCD displays to have between 130- and 140-degree viewing angles. So there persists a noticeable difference between the two technologies when viewed in real world situations (up and down, side to side).

Advantage: Plasma

FUNCTIONAL CONSIDERATIONS:

hal met lcd scherm

COMPUTER USE

LCD monitors display static images from computer or VGA sources extremely well, with full color detail, no flicker, and no screen burin-in. Moreover, the number of pixels per square inch on an LCD display is typically higher than other display technologies, so LCD monitors are especially good at displaying large amounts of data-like you would find on an Excel spreadsheet, for example-with exceptional clarity and precision.

Plasma, on the other hand, does not handle static images especially well insofar as "burn-in" is still a major issue with these monitors, as is distortion resulting from lower-resolution panels displaying static images at expanded sizes. Finally, while video images look good on plasmas, there can be some flicker, depending on the quality of the unit and the resolution it's displaying.

Advantage: LCD, except at "harsh" viewing angles.

VIDEO PLAYBACK

Plasma displays get the nod here because of their excellent performance with fast-moving images, high contrast levels, color saturation, and overall brightness.

While the "response time" of LCD TVs has markedly improved in the last couple of years, they still suffer from a slight "trailer" effect, where the individual pixels are just slightly out of step with the image on the screen.

Advantage: Plasma

USING YOUR UNIT AT ALTITUDE

There is a reason why LCD panels are the preferred visual display units for use on airplanes: LCDs aren't affected by increases (or, for that matter, decreases) in air pressure. Their performance is consistent, regardless of the altitude at which they're utilized.

Not so for plasma TVs. The display element in plasma TVs is actually a glass substrate envelope with rare natural gases compressed therein. So, at high altitudes (6500 feet and above), an air-pressure differential emerges, which causes plasma displays to emit a buzzing sound. Increases in the amount of power required to run the unit and heightened stress on fans to cool it are the root of this buzzing noise, which sounds rather like the humming of an old neon sign.

Advantage: LCD, at 6500 feet and higher.

LONGEVITY

LCD manufacturers claim that their displays last, on average, 50,000 to 75,000 hours. In point of fact, an LCD TV will last as long as its backlight does-and those bulbs can actually be replaced! Since this is nothing more than light passing through a prismatic substrate, there is essentially nothing to wear out in an LCD monitor.

Plasma, on the other hand, utilizes slight electric currents to excite a combination of noble gases (i.e., argon, neon, xenon), which then glow red, blue, and/or green. This is an essentially active phenomenon, so the phosphoric elements in plasma displays fade over time. The half-life of these gases is approximately 25,000 to 30,000 thousand hours. At this point, the phosphors will glow half as brightly as they did when the set was new. There is no way to replace these gases; the display simply continues to grow dimmer with use.

Advantage: LCD x 2. LCDs are especially good for long-haul applications like 24/7 signage.

SCREEN INTEGRITY

LCD technology is not prone to screen "burn-in" or "ghosting" the way plasma technology is. On plasma displays, static images will begin to "burn-in," or permanently discolor the pixels displaying it, after only a short time-just 15 minutes or so, in some cases. Though such "burn-in" can be reduced or "washed out," doing so reduces the overall lifespan of the display unit itself.

Advantage: LCD

OTHER CONSIDERATIONS:

PRODUCTION SIZE & COST

Though both plasma and LCD panels are difficult to produce in large sizes, plasma has proved the easier of the two to manufacture in the 60- to 63-inch category. Though such mammoth monitors are expensive, they exhibit none of the "kinks" one might expect with such large displays. In other words, even the largest plasma displays are reliable.

The substrate material for LCD TVs has proved difficult to produce in large sizes without pixel defects owing to faulty transistors. NEC produces the larges LCD display at the moment, and it measures 40" diagonally. Sharp has begun to mass-produce 37-inch widescreen LCD panels.

Advantage: Plasma. Even though production costs and retails prices have come down for both technologies, plasma still has the edge as far as production cost and capacity go.

VOLTAGE REQUIREMENTS

Because LCDs use florescent backlighting to produce images, they require substantially less power to operate than plasmas do. LCD displays consume about half the power that plasma displays consume. The reason: Plasmas use a lot of electricity lighting each and every pixel you see on a screen-even the dark ones. These are truly power-hungry devices.

Advantage: LCD x 2.

Een uitgebreid artikel nederlandstalig over plasma en LCD schermen vind u onder andere op www.zdnet.be

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