So what about the LCD, today’s most obvious alternative to plasma? A liquid-crystal television is, in effect, a sandwich with many ingredients. Its layers include a bright white backlight, a layer of liquid-crystal molecules, a matrix of thin-film transistors, two pieces of polarized glass, and colored filters. The transistors control the voltage applied to the three groups of liquid-crystal molecules that make up each picture element.

When the voltage is on, it twists the molecules, allowing light through the layers of glass and color filters; the molecules untwist when the voltage is off, blocking light. Each picture element consists of liquid-crystal molecules above a red, a green, and a blue filter. Switching the appropriate molecules on and off gives myriad combinations of red, green, and blue light, and therefore the palette of human vision.

Because of this many-layered structure, liquid-crystal TVs start off with a relatively poor contrast ratio—the difference between the brightest white and the darkest black that the screen can display. The white backlight that illuminates the displays is usually a cold cathode fluorescent tube, which operates on the same basic principles as the ubiquitous and venerable neon sign. The light has a rough path to travel through the many layers before it reaches the viewer’s eyes. Each layer absorbs some of the light, leading to reduced contrast and brightness.

LCDs are basically reliable. The component that limits their life is the backlight. The fluorescent tubes age over time; after about five years of normal home use, the tubes start to dim and their color temperature starts to drift—that is, the hue of the emitted light shifts from clean white toward the red end of the spectrum. The shift is gradual; viewers usually don’t notice the change until it is extreme. Because of this aging of the fluorescent tubes, the average usable life of a liquid-crystal TV is about seven to 10 years—close to that of ordinary CRT-based TVs.

To improve the longevity of liquid-crystal TVs, some manufacturers have recently started to use high-intensity light-emitting diodes (LEDs) as backlights. They aren’t cheap, though prices will come down as manufacturing volumes go up. Samsung sells a 46-inch model for about $9000; Sony is selling a similar set for about $12 000. In these models, instead of a fluorescent lamp, an array of red, green, and blue LEDs creates what appears to be white light.

Besides increasing the usable lifetime of an LCD, this LED-based lighting increases the color saturation of the display. Saturation is basically the purity of a color, or, more precisely, the relative bandwidth of the light. Light emitted at tighter bandwidths is more saturated; light occupying wider bandwidths looks washed-out.

When the color filters on an LED-illuminated display remove blue and green to display a red pixel, for example, the resulting red is at the single red frequency originally generated by the red LEDs. Do the same filtering to display red on a fluorescent-illuminated display, and a wide range of red frequencies creates a less-saturated color.

Saturation is particularly important for large high-definition liquid-crystal panels bigger than 37 inches, because picture-quality problems are more pronounced in larger panels. Increased saturation allows finer gradations of colors, enabling pictures to seem startlingly vivid, an effect particularly striking in scenery. A surfer on a red board pops out in a vast blue ocean; it’s the kind of imagery that might even get you addicted to the Travel Channel.

But even LEDs don’t last forever. Degradation starts becoming noticeable after about 60 000 hours of use—for most people, that means roughly 15 years. Although these LED/LCD televisions incorporate sensors to measure and adjust their hues as the diodes age, they, too, after about a decade of moderate use, will fade and the panel will dim. And they consume about twice as much power as conventional fluorescent-lit LCDs. A 42-inch LCD backlit with LEDs runs at around 250 to 300 watts, only a little less than a plasma panel.

Pretty soon—in about two years—there will be a third horse in this race. The surface-conduction electron-emitter display, or SED, is just now starting to emerge as a serious contender in the race to replace the CRT. SED is an alternative flat-display technology emerging from Canon and Toshiba.

In an SED [see diagram, “SED Science”], every single pixel of the display is, effectively, a cathode-ray tube. The cathode is a thin film of palladium oxide, chosen because it is electrically conductive and also extremely durable, resisting oxidation and corrosion even at high temperatures. As in a CRT, electrons emitted from the cathode hit phosphors—tiny dots of metals or rare-earth compounds that glow red, green, or blue when energized.

The result is a flat-panel display that uses less energy than a plasma screen does and yet has image quality close to that of the CRT, still the benchmark of all displays. Power consumption is low, relative to that of plasma, for the same reason as it is for the CRT: it takes a lot less energy to create an electron beam than it does to excite photons in a gas.

SED is a variation of field-emission display technology [see “Watching the Nanotube,” IEEE Spectrum, September 2003]. The main difference is that SED, for its cathodes, uses ­palladium-oxide film rather than the cone-shaped bundles of carbon ­nanotubes employed in field-emission displays. (Nanotube-based field-­emission displays have, so far, proven difficult to manufacture, mainly because of the difficulty of producing the nanotubes.) SEDs theoretically have a manufacturing advantage because they can be printed using an industrial inkjet printer not that much different from the inkjet printer in your home or office.

Last year, Toshiba and Canon began trial production of surface-conduction displays in the 40- to 50-inch range. Despite the theoretical manufacturing advantage, the companies appear to be having issues in bringing yields up to a commercially viable level. They say they’ll start mass production next July and ship SED televisions to Japanese retailers later in 2007.

The first SED televisions are likely to cost about 50 percent more at retail than comparable plasma sets. At the moment, it is not clear whether they will suffer from any long-term reliability or performance issues. Next year we should know if surface-conduction technology has a real chance of carving out a significant niche for itself; if Canon and Toshiba can’t make a reliable product in high enough volumes at a realistic retail price, the market just won’t buy into the technology.