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January 23, 2007 > TechKnow Talk

TechKnow Talk

LCD, Plasma, or Projection: Which TV is Best?

Didn't get that big-screen television for Christmas? Looking to upgrade for the Super Bowl? With the relatively recent advent of flat panel TVs, as well as HDTV and related technologies, shopping for a TV has become confusing. The hype and misinformation promulgated by manufacturers and retailers doesn't help.

First, let's take a quick look at the underlying technology of each type of TV, highlighting the differences, and identify the strengths and weaknesses of each. For the impatient reader, a very short answer to the question of which type is best appears in the final paragraph.

CRT (Cathode Ray Tube) technology has been around since the 1930s, though of course it has been refined since then. A CRT works by creating a stream of (negatively charged) electrons at a hot filament (cathode) and accelerating them through a vacuum tube onto the inside of a positively charged glass screen (anode). The beam is directed over the screen in a raster pattern, or line by line, illuminating each point, or picture element (pixel), on the screen many times (typically 30) each second. The screen is coated with phosphors, which glow when excited by the electron beam. Phosphors that emit red, green, and blue light are used in combination, by varying the intensity of the beam on each, to generate all the colors of the spectrum at each pixel.

Despite being "old technology," CRT televisions produce outstanding picture quality with excellent reliability. However, as they increase in size, the thick glass screens become very heavy. They must also be made deeper, to accommodate a longer electron gun able to direct the beam to every point on the larger screen. Thus there is a practical limit to the size of CRT televisions, and due to the increasing demand for larger screens, the CRT may be headed for extinction in the home TV market.

LCD (Liquid Crystal Display) televisions utilize a matrix of liquid crystals arrayed on the inside of the screen, capable of aligning themselves to transmit or block light, based on the electrical signals they receive at each pixel. As in CRTs, there are three elements associated with each pixel, but in LCDs, no light is generated by these elements. Instead, each red, green, or blue element transmits or filters out component wavelengths of a white fluorescent light source to create the requisite colors.

The term "liquid crystals" is something of a misnomer. The molecules are not actually liquid, but are pliable enough to deform or twist in response to electrical stimulation to block or transmit light. A sophisticated control technology, called active matrix, is used to manage the liquid crystals. Thin film transistors (TFTs) provide very precise electrical commands necessary for the LCD to produce rapidly changing video images.

Plasma TVs are the primary competitors to LCDs. The technology involves an array of tiny gas bubbles sandwiched between two glass plates. The bubbles contain argon, xenon, or neon in a plasma, a state in which electrons have been stripped free of the atoms. Exciting these bubbles with electrical current causes them to emit ultraviolet light. This light in turn causes phosphor coatings on each bubble to fluoresce. Each pixel contains three bubbles, each coated with an appropriate phosphor to produce the desired color: red, green, or blue. The magnitude of electrical charge fed to each bubble determines the intensity of the glow produced by the corresponding phosphor element, in combination blending any desired color.

Plasma technology is easily scaled. That is to say there is no great technical challenge in making larger screens and the electronics used to drive them. For this reason, plasma TVs are preferred over LCDs for very large screen sizes. Plasma screens are also very thin, offering the advantage of taking up little space, and are often wall-mounted. But they are heavier than LCDs. A 42-inch plasma screen weighs about 100 pounds.

A third option for consumers is projection television systems. These TVs typically use CRT or LCD technology to create a relatively small, high quality image, then magnify and project this image onto a screen. Front projection televisions project the image onto the front of an external screen, as in a movie theater. Rear projection systems project the image onto the back of a screen, often within the same enclosure as the TV and projector, giving the effect of a large television.

While high-end front projection systems can render a quality display in large screen format, most consumers don't want the trouble or expense of a multiple-component system. In addition to the CRT or LCD source, a projector, screen, audio system, and TV tuner are required. Significant installation work may also be required. The rear projection TVs tend to be big and bulky, but many are integrated systems and can offer a large image at lower cost than plasma TVs.

So which type of television is best? It depends on the needs of the consumer. Televisions of excellent quality are available in both LCD and plasma at competitive prices, but there are some pros and cons to each.

Large LCD screens are difficult to manufacture, so if you desire a TV larger than about 42 inches, plasma offers better options. This is beginning to change, as LCD manufacturers are starting to field larger screens, but the long-term reliability of these large LCDs has not yet been proven. LCDs are about 30% more energy efficient, though the cost of operation may not be a decisive factor for most consumers.

Plasmas are heavier, and are susceptible to burn-in, a permanent shadowing of the screen resulting from an image being displayed for a long period of time. This is more likely to be an issue with computer screens than TVs, which are typically turned off when not in use. But if the TV will also be used as a computer monitor, LCD is the best option.

Plasma TVs generate superior contrast and color reproduction, especially in dimly lit rooms. This is what elicits the "wow factor" when customers first see a large plasma TV. But it may not look the same in a living room as it does in the showroom. Because they are very bright and handle glare better, LCDs are preferable to plasma for brightly lit or sunny rooms.

Plasma screens are viewable from a broad range of angles. LCD image quality drops off as the viewer moves left/right or up/down of directly in front of the screen, though the effective viewing angle is much better with current LCD models than it was just a couple years ago. Still, if the TV will be used in a room where viewers are spread across a wide angle, plasma is the better choice.

LCDs have higher resolution for a given screen size; there are more pixels per square inch. This also begs the question of High Definition (HD), and whether there is sufficient programming to justify buying a TV capable of true HDTV. The answer is yes. There is considerable HDTV available now on cable, satellite, and DVD, and there will be much more in the coming years. Technologies such as Enhanced Definition (ED) are not true HD, though they are able to display an HD signal at lower resolution. Currently, the higher native resolution of LCDs gives them an edge over plasma in HDTV.

There has been a lot of hype about the longevity of LCD over plasma. LCDs do tend to last somewhat longer than plasma TVs. However, this should be considered in context. The quality of both LCD and plasma displays will degrade with usage. With time, LCD light sources dim and change color, while plasma phosphor coatings glow less brightly.

The LCD may maintain a quality picture slightly longer, but only if a quality, name-brand bulb is used, and such sets are more expensive than comparable plasma TVs. Inexpensive LCD TVs usually mean cheaper light sources and faster degradation of the image. And manufacturers of plasma TVs are quickly closing the longevity and image degradation gap. In any case, a high-end TV of either type should provide some 50,000 hours of viewing, which is 20-30 years, even for a TV junkie.

To summarize, if the most important factors are large screen size, outstanding contrast and color, and a range of viewing angles, a plasma TV is the best choice. If light weight, reduced glare, high resolution, and application as a computer monitor are your criteria, go with an LCD. If you seek a very large screen at minimum cost, and can tolerate a large, bulky unit, consider a rear-projection TV.

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