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THE FRONT LINE: MAY 15, 2005 |
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| FLAT-PANEL MONITORS AND URBAN LEGENDS As I sit here in my studio and read the latest research and market price information on LCD and plasma monitors, I have to remind myself that only a decade ago, these products weren’t even a blip on anyone’s radar in the production community. Indeed, the earliest 42-inch plasma monitors had staggering price tags (over $15,000) and were more architectural curiosities than practical display solutions. Ah, but the market has worked its magic. At every trade show you attend this year, you will see ample quantities of LCD and plasma displays in all size adorning trade show booths, being hawked for everything from reference monitors to client lounges. You’ll see all kinds of input configurations (analog and digital), outboard media servers, stands, wall brackets, rack mounts, and accessory speakers to go with them. We all know that LCD and plasma TVs are fast becoming popular in the consumer TV marketplace, whether they dominate the family room or hang under a cabinet in the kitchen. And they are starting to show up in production houses as well, most commonly in screening rooms or waiting areas. As with any new technology, there are the associated myths that go with LCD and plasma displays. Can’t let LCDs freeze. Plasmas burn in. Plasmas buzz at high altitudes. The gas leaks out of plasma monitors over time. LCD displays can burn-in, too. LCD monitors have horrible black levels. No doubt you’ve heard one or more of these tales recently. So, it’s probably a good time to see what if any truth lies behind them. Plasma Burn-In: Plasma displays work by generating lots of power to activate each of their tiny gas-filled pixels. (You might be surprised to know that a typical 50-inch monitor can consumer over 500 watts in normal operation!) The discharge of high voltage is what makes the phosphors in each pixel glow and form images. Unfortunately, there is no way to make this a low-voltage process. And it became obvious early on to plasma manufacturers that the phosphors would degrade quickly if the panel was operated at high levels of brightness. The problem was further aggravated by static images (usually text) that rapidly aged phosphors, leaving a permanent ghost image of them on the screen when the plasma monitor was turned off. While burn-in was a problem not too long ago, the current crop of plasma monitors and TVs uses a different gas mixture (more xenon, less neon) as well as an improved pixel shape to yield more light at lower power levels. You’ll hear predictions of 60,000 hours in sales sheets, but even you conservatively cut that to 30,000 hours, it really is a non-issue. However, you still want to avoid showing bright, static images on any plasma display for long periods of time. Plasma ‘buzz’ and leakage: The discharge of voltage through each plasma pixel not only creates a burst of ultraviolet light (and a broad spectrum of electromagnetic ‘garbage’); it also causes a small mechanical vibration. Ever been close to a neighborhood power transformer when it shorted out? Remember that big ‘thump’ you heard and felt in the ground? Same principle. We really don’t notice this mechanical vibration or ‘buzz’ at low altitudes because the air pressure is high enough on the glass surfaces to minimize it. But go up in altitude where air pressure is lower, and you will definitely hear it. The glass is not separating: it’s just free to vibrate more vigorously. And it should be noted that the glass enclosures for plasma monitors are sealed at the factory to withstand several air pressures from within and without. Unless you crack the doggone thing, the neon/xenon mixture will remain safely inside for a long, long time. LCD monitors freeze at low temperatures: Well, at some point, everything will freeze! But the liquid-crystal paste used in LCD displays has a different specific gravity than water, and its freezing point is much lower as a result. I have left consumer and professional LCD monitors out in cars overnight when temperatures dropped into the low ‘teens with no adverse effects the next day. (Be nice to the monitor and let it warm up to room temperature before use.) Keep in mind that many of the displays in today’s cars use LCD technology, in particular car radios and CD players. When was the last time you saw one of those crack when left out in cold weather? LCD monitors can burn-in: Impossible! The process by which an LCD display creates images is to change the position of individual liquid crystals in each pixel and block or pass light through them. There is no high-voltage, high-energy discharge; the liquid crystals rotate into different alignments as the low voltages in each cell change. However, each pixel behaves like a capacitor, and a residual charge can build up inside that tiny capacitor if the pixel remains in the same state for a long time. As a result, the stored charge locks the liquid crystals into one position, even after the monitor is turned off. A quick flash to an all-white screen followed by a black screen clears this residual charge and solves the problem. LCD monitors have horrible black levels: Well, LCD ‘black level’ (no signal) measurements are not nearly as good as that of a plasma or CRT monitor for certain. The best I’ve seen so far is somewhere in the range of 1.5 – 2 nits, as opposed to the .2 nits readings from a top-notch CRT display. But there is a way around it – simply reduce the brightness of the backlight. Newer LCD TVs and monitors are now coming out with adjustable backlight controls, letting you optimize the display’s grayscale for ambient room lighting. Higher black levels aren’t really noticeable under normal room light, but they do jump off the screen when lights are dimmed. Make sure you have a multi-step grayscale test pattern on hand before you make this adjustment so that you don’t ‘crush’ black and low shades of gray. Contrast will still be good and you will be surprised at how much lower those ‘black levels’ will become. |
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