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Some of the display technologies for HDTV have different properties which some consumers may want to consider before buying a HDTV monitor. Plasma flat screen displays and flat screen LCD displays are two of the more prevalent technologies available today in retail stores. Here are some of the properties to consider:

Plasma displays have a lot higher power consumption than LCD, typically in the region of two-and-a-half to three times. Much of that gets translated into heat. Along with the higher utility costs associated with the higher power consumption, there’s the potential for increased levels of noise. Most of the larger plasma displays have fans. In a home theater situation you may not want this background noise when a silent or quiet scene in a movie is disturbed by the fan noise, although some plasma monitors now can use variable speed fans that stay off until a certain temperature is reached.

Typically with plasma, you’re switching 200 to 300 volts, and you’re switching it very fast. In LCDs, you’re switching 5 to 12 volts. That’s a very big difference. The heat and voltage requirements directly affect the size of the cabinet and its internal electronics. The electronics that drive an LCD weigh a small fraction of the electronics needed to drive a plasma, partly because of the high power and high heat dissipation. Other comparisons stem directly from the fact that these are radically different display technologies. Plasma is a phosphor-based device, while LCD is a transmissive device.

The light is actually reflected through the LCD, where with plasma, the phosphor is ignited and that causes the colors for your display. It takes longer to light up a liquid-crystal pixel than it does to light up a phosphor, so a plasma monitor has a faster response time than an LCD monitor. When displaying moving images, plasma is going to have fewer artifacts. LCDs, even the best on the market today, will have some degree of trailing edge blur, because the response time of the liquid crystal is relatively slow.

Plasma inherently has no gray scale. It’s either on, or it’s off. To get intermediate shades of gray, you have to use time-division techniques. Instead of turning a pixel on for a full period of time, you turn it on for half a period, and you get half brightness, which our eyes integrate over that time and average out. If the plasma manufacturer slows down the switching too much, there can be a noticeable strobing. Only the most sensitive people will see the strobing effects. Obviously, the more often you switch things, the more power you use. So there’s a trade-off here. 

Technology differences also affect the rate at which costs go down. Plasma uses tiny little light bulbs, as opposed to LCD which uses tiny little transistors. We can make transistors very, very small. The industry has a very good expertise in doing that, from microprocessors and now LCD technology. But it’s more difficult to make very, very small light bulbs. Because of this difference, LCD prices are likely to fall faster than plasma prices. Over time, LCD screens could drop to the same price—or even become less expensive—than same-size plasma screens.

 The smaller and better transistors found in LCDs give them another advantage over plasma screens: resolution. Right now, a 30-inch LCD can have a native resolution of 1,280 by 768. You can’t produce a 30-inch plasma with that resolution. LCDs are likely to hold that advantage for the long term. LCDs have an edge over plasma in terms of resolution. Almost all the 40- to 42-inch plasmas that are on the market have a pixel format in the region of 860 by 480 pixels. The 40-inch LCD is 1,280 by 780, which fits right into the high-definition television market.

Even if larger-sized LCDs continue to be more expensive, some buyers may choose it over a lower-priced plasma of a comparable size, simply because they need the higher resolution. For some monitor buyers, image quality is job one. Here, plasma and LCDs offer a mix of plusses and minuses. 

Plasmas tend to have a higher contrast than LCDs. Plasmas can have a 1,500:1 contrast ratio. LCDs are hovering somewhere around 400:1. Plasma also has advantages in the purity and distribution of the colors. From corner to corner, plasma is more even, as far as brightness and color uniformity goes. With LCDs, that can vary a little bit due to the transmissive nature of the light going through the LCD and the different depths or diameters of the LCD panel itself. If the LCD backlights are improperly mounted, they can contribute to an unevenness of the brightness levels and to a drop-off of color saturation in some areas of the display.

LCD takes the honors for having the blackest blacks. When you look at a plasma screen, you’re really looking at the phosphors, and phosphors reflect light. The ambient light hits the phosphors, and although the phosphors aren’t being excited, they’re still relatively good reflectors of ambient light. Our eyes see that as a mid-to-darkish gray, but certainly not as black. New vertically aligned technology, such as PVA (Patterned Vertical Alignment), can produce LCD screens where the black actually is black.

Whether blacker blacks are essential may depend on your application for the monitor. If you want good video viewing or good game viewing, having blacker blacks is quite important. LCDs are intrinsically better than plasma in doing that. Plasma could improve by putting selective filters on the front, but that will impact the power, because not only are you going to filter out the ambient light, but that will lose some of the transmitted light, as well. So there’s a trade-off.

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