Outward appearances are definitely deceiving when it comes to LCD and Plasma televisions. Although both types of televisions are flat and thin, they employ different technology in an attempt to deliver similar results.
Plasma TV Overview
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Plasma television technology is based loosely on the fluorescent light bulb. The display itself consists of cells. Within each cell two glass panels are separated by a narrow gap in which neon-xenon gas is injected and sealed in plasma form during the manufacturing process. The gas is electrically charged at specific intervals when the Plasma set is in use. The charged gas then strikes red, green, and blue phosphors, thus creating a television image. Each group of red, green, and blue phosphors is called a pixel (picture element).
Although Plasma television technology eliminate the need for the bulky picture tube and electron beam scanning of traditional televisions, because it still employs the burning of phosphors to generate an image, Plasma televisions still suffer from some of the drawbacks of traditional televisions, such as heat generation and screen-burn of static images.
LCD TV Overview
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LCD televisions, on the other hand, use a different technology (see also question #1 for this same explanation).
Basically, LCD panels are made of two layers of transparent material, which are polarized, and are "glued" together. One of the layers is coated with a special polymer that holds the individual liquid crystals. Current is then passed through individual crystals, which allow the crystals to pass or block light to create images. LCD crystals do not produce their own light, so an external light source, such as florescent bulb is needed for the image created by the LCD to become visible to the viewer.
Unlike standard CRT and Plasma televisions, since there are no phosphors that light up, less power is need for operation and the light source in an LCD television generates less heat than a Plasma or traditional television. Also, because of the nature of LCD technology, there is no radiation emitted from the screen itself.
Plasma Television Advantages
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For Plasma televisions, the advantages over LCD, are: Better contrast ratio, better ability to render deep blacks, more color depth, better motion tracking (response time), and more availability in very large screen sizes.
Plasma Television Disadvantages
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However, the disadvantages of Plasma vs LCD include: more susceptible to burn-in (although this is not as much of a factor now, due to technology improvements in the past couple of years), more heat generation, does not perform as well at higher altitudes, and shorter display life span (although this too is changing due to technology improvements), heavier weight, and more delicate to ship.
LCD Television Advantages
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LCD television advantages include no burn-in susceptibility, cooler running, less screen glare, more functional at high altitudes, longer display life (although improvements are being made in Plasma screen life), looks better in brightly lit rooms.
Also, LCD televisions have made great strides in upping-the-ante in native pixel resolution, with a growing number of sets offering a full 1080p (1920x1080) display capability at affordable price levels in screen sizes ranging from 37-inches and up.
On the other hand, the number of Plasma Televisions offering 1080p native pixel resolution are still few and far between, as well as being more expensive in comparison to their LCD counterparts.
One factor to consider in favor of LCD over Plasma (at least for the near future) is that if you are planning to purchase a Blu-ray Disc, HD-DVD, or Upscaling DVD Player, LCD may be a more cost-effective option as you can get a 1080p LCD set from 37-to-42-inches at a lower price than and 42-inch size Plasma set that has 1080p resolution.
One other factor to consider is that LCD televisions are typically lighter (when comparing same screen sizes) than their Plasma counterparts, making wall installation easier.
LCD Television Disadvantages
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LCD televisions do have drawbacks in several areas vs Plasma televisions: Lower contrast ratio, not as good rendering deep blacks, not as good at tracking motion (although this is improving), and not as common in large screen sizes above 42-inches (although the number is growing).
Also, although LCD televisions do not suffer from burn-in susceptibility, it is possible that individual pixels on an LCD televisions can burn out, causing small, visible, black or white dots to appear on the screen. Individual pixels cannot be repaired, the whole screen would need to be replaced at that point, if the individual pixel burnout becomes annoying to you. Finally, LCD televisions are more expensive than an equivalent-sized Plasma television, although the price gap is closing.
The Mercury Issue
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Also, one argument that Plasma Television manufacturers are making about LCD Televisions is that they use mercury as part of the chemical makeup of the florescent lighting used to illuminate the screen surface.
However, this is a red herring with regards to choosing a Plasma Television over an LCD Television. In LCD sets, the amount of Mercury used is not only small, it never comes in contact with the user. Also, keep in mind that most common high-efficiency florescent lamps also use Mercury.
Mercury is one of the Earth's elements; its existence in nature is a part of natural processes and has both beneficial and non-beneficial uses, just as most other elements and chemical compounds. You are probably in more danger eating Fish, that may contain traces of Mercury, a couple of times a week than watching, touching, or using an LCD TV. Also, with the development of LED lighting sources, which is Mercury-free, this issue will resolve itself in the years ahead.
LCD Television and HDTV Reception
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On the HDTV part of the equation, most LCD televisions already have built-in standard TV tuners (HDTV tuners must usually be added externally - but more are showing up as a standard feature), while many Plasmas are just monitors-only and may require both external standard and HDTV tuners to receive television signals (although more are beginning to include either NTSC and/or both HDTV tuners). This is definitely a point to check when making your buying decision as it will affect your budget.
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My recommendation is to go to a dealer and really take a look carefully at several Plasma and LCD televisions and compare the performance based on the above factors and narrow down your choices to one or two of both types and make your decision based on what type will give you the most pleasing image, connection flexibility, and fits your overall budget expectations.
However, both Flat Panel Plasma and LCD televisions are viable options for home theater, and, with prices continuing to come down and features and quality continuing to go up, both types are quickly becoming a good value for consumers