So which technology will dominate over the next four to five years? Two winners will emerge, one for screen sizes smaller than 50 inches, one for screen sizes larger than 50 inches. Fifty is the magic number in the TV business, because it is, at least today, the upper limit for economical production of reliable panels that lay electronics on a glass substrate. It is also, not coincidentally, the smallest projection television screen size in mass production today.

For screens smaller than 50 inches, which account for the vast majority of sets sold throughout the world, the two most attractive technologies will be LCD and, conceivably, SED. But the prices of the SEDs are not likely to come down significantly before 2010. So the near-term winner will be the LCD.

Liquid-crystal technology will dominate not only the under-37-inch, or small-TV, category but also the midsize segment of 40- to 50-inch TVs. The lower cost and long-term reliability of LCDs will make them a better value than SEDs or plasma displays.

For consumers looking for the largest screens, those bigger than 50 inches, projection TVs are going to be the best bet for the near future. As plasma, liquid-crystal, and surface-conduction display sizes increase, yield goes down and therefore cost goes way up. A manufacturing line that produces four 42-inch displays at a time can manufacture only one 100-inch display, and that large display is more likely to have faulty areas, reducing yield. Nevertheless, 103‑inch plasma screens will soon hit the market, as will 65‑inch LCDs. But the prices are going to be ­ridiculous—about $70 000 and $15 000, respectively.

Projection TVs have gotten better lately. If you wince at the memory of the shadowy, washed-out images of the projection TVs of 20 years ago, you’re in for a surprise. Today’s projection technologies include Digital Light Processing (DLP) from Texas Instruments and micro-LCD and liquid crystal on silicon (LCOS) used in TVs from Hewlett-Packard, JVC, Mitsubishi, RCA, Sony, Samsung, and others.

Of the 10 million projection televisions that Gartner estimates will be manufactured this year, 25 percent are expected to be based on DLP, 9 percent on LCOS, and 66 percent on micro-LCD. All three technologies offer pictures both brighter and sharper than those viewed by moviegoers at traditional cinemas today. Many models also display deeper blacks and correspondingly higher contrast than most LCD or plasma displays.

A high-definition DLP system contains an array of just over 2 million hinge-mounted micromirrors, each about 20 square millimeters. A bright white light shines on the array. The mirrors change orientation to either reflect light to the screen or not—that is, to make an individual pixel light or dark on the screen. The mirrors, controlled by microscopic electrodes, switch up to several thousand times per second.

The system coordinates the switching with the rotation of a single color wheel, typically 7 centimeters in diameter, enabling the mirrors to create the red, green, and blue components of every one of the millions of pixels in a television image. To keep up with the 30-frame-per-second refresh rate of National Television System Committee (NTSC) video, the wheel has to move precisely and fast—first-generation color wheels, with three color segments, rotated at around 3600 revolutions per minute. Today’s color wheels, with seven color segments (two each of red, green, and blue, plus one of white) rotate at about 7200 rpm [see illustration, “Mirror, Mirror”].

LCOS displays also redirect reflected light to create the television image, but they use individual liquid crystals to do so instead of micromechanical mirrors. The liquid crystals coat a reflective surface, typically on a 15-mm2 silicon chip, and change their orientation to block or allow the light to reach that reflective surface. In single-chip LCOS systems, either a color wheel or an array of LEDs illuminates the LCOS chip. In multichip LCOS technology, three separate chips, one for each primary color, combine optically to produce the visible image.

The third competing projection technology, micro-LCD, uses three transparent LCDs, one each for the red, green, and blue components of a full-color image. Each LCD measures from 18 to 33 mm diagonally, depending on the particular manufacturer and model. Mirrors split light from a metal-halide lamp into red, green, and blue beams, sending each beam of light through the appropriate LCD. The three beams pass through the LCDs into a prism, which combines the light back into a single beam to form a full-color image.

Each of these technologies has minor drawbacks. The heat from the high-intensity metal-halide projector lamp, over time, degrades the liquid-crystal coating in the micro-LCD panels, discoloring the TV picture. The spinning color wheel of single-chip DLP and LCOS systems can create a rainbow effect for some viewers, because it depends on the human vision system to retain images instantaneously after they are actually no longer visible and thus merge the red, green, and blue images into one. Some people’s eyes adjust better than others’. The rainbow is most noticeable when the picture has a lot of contrast, like a candle on a black background. In a football match with lots of motion and detail, the rainbow effect is hardly noticeable.

And all projection systems share one major problem: the lamp.

Projection systems typically use metal-halide projector lamps, because they are bright and give a consistent color level and brightness over their lifetimes. These lamps produce light by passing an electric arc through a high-pressure mixture of argon, mercury, and a variety of metal-halide gases. The precise mixture of halides affects the nature of the light produced, influencing the correlated color temperature and spectral intensity (making the light bluer or redder, for example).

The argon gas in the lamp is easily ionized, creating the arc across the two electrodes. Heat generated by the arc vaporizes the mercury and metal halides, which produce light as the temperature and pressure increase. About 24 ­percent of the energy used by metal-halide lamps produces light, making them generally more efficient than fluorescent lamps and substantially more efficient than incandescent bulbs such as halogen.

But these lamps last only 1000 to 2000 hours, and they are not cheap to replace, at $300 to $400 each. Longer-life lamps are available, such as the ultrahigh performance (UHP) lamps invented by Philips. These lamps generate an arc in a nearly pure mercury vapor under high pressure. The arc gap can be much smaller than that of alternative lamp technologies, as small as 1.3 to 1.0 mm across.

The smaller gap is more efficient; a 100-W UHP lamp in a projector can deliver more light to the screen than a 250-W metal-halide lamp. UHP lamps range from 100 to 200 W, with useful life spans ranging from 3000 to 10 000 hours. They are now available in video projectors and rear-projection TVs from all the major manufacturers.

But like LCD manufacturers, projection television manufacturers are moving toward replacing lamps with high-intensity LEDs, likely to be pervasive within the next three or four years. These LEDs will not be cheap either, but they should offer lifetimes measured in tens of thousands of hours. Such lifetimes will make the maintenance and operating costs of projection systems comparable to those of other available television displays.

Projection TVs are also smaller than they used to be: the boxes containing the projection optics and electronics are a lot shallower than their predecessors of 20 years ago, thanks to microdisplays’ replacing the earlier large-tube technology. As a result, the average depth of a projection television with a 50-inch screen today is only 0.43 meter.