Photo by Tony Cordoza
All diagrams by Dimitry Schidlovsky except for the LCD which is by Mark Schrieder.
Given that cathode-ray tubes (CRTs) provide the best pictures, why are so many companies moving away from tubes and into new technologies? Because that's how they can make the thinner and lighter TVs everybody's clamoring for. It doesn't matter whether you're talking about plasma, digital light processing (DLP), liquid-crystal display (LCD), or liquid crystal on silicon (LCoS)-all four roads lead to a new generation of video displays that leave heavy and bulky CRT-based TVs behind.
To make shopping for a new TV a little easier, we've assembled a brief introduction to these four cutting-edge display technologies-all of which are working hard to trump the tube. Plasma, DLP, LCD, and LCoS are all "fixed-pixel displays"-electronic screens made up of a grid of square or rectangular pixels (short for "picture elements"). You already rely on this kind of display in your digital watch, cellphone, and laptop. Over the past few years, lots of people have reclaimed desktop real estate by trading in their clunky CRT computer monitors for flat, fixed-pixel screens, and the same display technologies are also starting to catch on for watching TV or DVDs in the living room, bedroom, and den.
Since plasma and direct-view LCD monitors are only a few inches deep, they can be hung on the wall like a picture frame. And unlike direct-view TV tubes, their depth doesn't increase proportionally with screen size. While DLP and LCoS can't be used to create flat-panel displays, they (along with LCD) can be used to make front projectors and rear-projection TVs (RPTVs) that are appreciably smaller and lighter than their CRT-based counterparts.
There's a simple reason why fixed-pixel TVs are thinner than tube models. In a CRT, a gun located at the back of the tube "scans" pictures line by line by firing an electron beam at phosphorescent material covering the tube's front surface. But the pixels in a fixed-pixel display are individually controlled points that can light up without the assistance of a scanning electron beam.
Fixed-pixel technologies have other advantages. For instance, while the three separate tubes used in CRT projection TVs need to be realigned periodically to preserve picture sharpness, fixed-pixel models require almost no maintenance. Another advantage is fixed resolution, which means you know exactly how many pixels are available to create an image. While the source material ultimately determines image quality, the more pixels a display contains, the higher its resolution. Fixed-pixel sets come in a range of resolutions, some as high as 1,920 x 1,080-enough to handle 1080i-format high-definition TV (HDTV) programs. If you combine all of these benefits with falling prices-both plasma and DLP prices have dropped precipitously over the past two years-it's clear that it will only be a matter of time before we say goodbye to the old picture tube.
What It Is
Everybody wants a plasma TV, and you only have to look at one to see why. Just 3 to 6 inches thick, plasma TVs can be set up adjacent to or mounted on a wall, preserving precious room space. And just because a plasma set is flat doesn't mean it can't be big. Screen sizes range from 32 inches diagonal to a cinematic 63 inches, making a plasma set a viable replacement for a tube-type rear-projection TV in small to medium-size home theaters.
How It Works
Each pixel in a plasma display consists of three gas-filled sub-pixels (cells) coated with red, green, or blue phosphors. A series of electrodes located above and below the cells (the top electrode layer is transparent) jolt them with varying amounts of voltage. This excites the gas in the cells, which in turn stimulates the phosphors to produce colored light.
•Uniformly bright picture over a wide viewing angle-even in a brightly lit room.
•Svelte design and large screen size.
•Many models have a wide 16:9 aspect ratio screen and a high enough pixel count to achieve HDTV-level resolution.
•On many sets, the black portions of the picture-for instance, dark shadows or the letterbox bars on widescreen movies-look dark gray rather than true black. A good tube TV generally produces better blacks than plasma models.
•Has the potential for burn-in, where an image becomes permanently etched onto the screen-but the danger of this happening is small unless you leave a bright stationary image on the screen for hours at a time. Newer models have burn-in prevention features like a "pixel orbiter," which exercises pixels by slowly shifting an image around the display.
Where It's At Just about every TV maker sells a plasma model. But due to high demand and relatively small manufacturing capacity, these slim, sexy sets are still expensive, with Gateway's $3,000 42-inch model representing the low end of the price scale. Expect to pay $3,000 to $5,000 for a 42-inch enhanced-definition (EDTV) model, $5,000 to $8,000 for a 42-incher that steps up to HDTV resolution, and $9,000 to $15,000 or more for a high-def model with a 50-inch or larger screen. Don't expect prices to fall to CRT levels for at least a few years.
What It Is
Fixed-pixel technology isn't just for flat TVs. Projection sets also benefit from it-especially rear-projection TVs, which can be slimmed down to a depth of less than 2 feet when chips are used in place of CRTs. One fixed-pixel technology, Texas Instruments' Digital Light Processing (DLP), offers a high-quality, inexpensive alternative to CRT for front projectors. But manufacturers are also starting to roll out more affordable DLP-based widescreen RPTVs.
How It Works
High-def DLP TVs use a small 16:9 chip, called a Digital Micromirror Device (DMD), packed with nearly a million "micromirrors" that reflect light from a lamp onto a screen. DLP sets fall mainly into two camps. Single-chip front- and rear-projection TVs filter white light from the lamp through a color wheel to produce color, while the more expensive ($23,000 and up) three-chip front projectors dedicate one chip each to the red, green, and blue primary colors. If the three tubes used in a CRT projector to beam an image onto the screen aren't kept perfectly aligned, the edges of lines will appear discolored. But since DLP images derive from a chip whose alignment characteristics don't "age," there's no need to tweak the picture periodically.
•While its reproduction of dark scenes isn't yet up to CRT standards, DLP achieves deeper, more realistic shadows and blacks than every other fixed-pixel technology. That's because the pivoting mirrors on a DLP chip create black by reflecting light away from the screen. Also, because the DLP mirrors are so close together, the sets generally don't have a problem with "screen door" effects (a faint image of the pixel grid).
•There is no danger of screen burn-in with DLP.
•DLP front projectors can be reasonably priced.
Cons•DLP rear-projection TVs are more expensive than the same-size CRT sets.
•Single-chip DLP sets are prone to a "rainbow" effect. Although the color wheel that separates the white light spins extremely fast, you may see streaks of primary color if you look closely enough, especially from one side of the image to the other. However, faster color wheels that can dramatically decrease this effect are appearing in newer sets.
Where It's At
Many manufacturers offer DLP-based TVs. Mitsubishi, Samsung, Panasonic, Hitachi, Zenith, and Sim2 Sèleco all sell rear-projection models, with prices starting at $3,999 for Samsung's 43-inch HLM4365W. RCA plans to introduce a 50-incher that lists for $4,499 later this year. But the most common DLP products are front projectors from companies like Runco, Sharp, DreamVision, Marantz, Panasonic, Yamaha, Plus, and Sim2 Sèleco. Basic projectors start at around $3,000, while HDTV-ready models range from $10,000 to $15,000. Prices of DLP sets have dropped every year, and the trend shows no signs of slowing down.
What It Is
The granddaddy of all fixed-pixel displays, LCD (liquid-crystal display) technology first appeared in pocket calculators in the early 1970s. It's an undisputed jack of all trades, capable of powering front projectors, rear-projection TVs, and flat-panel displays. LCD screens have already caught on in the computer world, but they've only recently begun to make headway in home theaters. This can be attributed in part to picture-quality issues. But there are also size limitations-until recently, flat-panel LCD screens maxed out at 30 inches (diagonal), although panels as large as 54 inches have been demonstrated.
How It Works
Whether spread across a flat-panel screen or placed in the heart of a projector, all LCDs are pretty much the same. A matrix of thin-film transistors (TFTs) supplies voltage to liquid crystal-filled cells sandwiched between two sheets of glass. As with plasma panels, a trio of red, green, and blue cells make up one pixel. When hit with an electrical charge, the crystals "untwist" to an exact degree to filter light generated by a lamp behind the screen (for flat-panel TVs) or one shining through a small LCD chip (for projection TVs).
•Direct-view models are only a few inches deep.
•LCD front projectors and RPTVs can deliver slightly better color than DLP sets because the three chips can be individually adjusted, although newer DLP models are narrowing the gap with six-segment color wheels that use two segments each for the red, green, and blue primary colors to improve color fidelity.
•Using the same wattage lamp, a typical LCD projector will create a brighter image than a DLP model-but most DLP projectors produce enough light for just about any home theater.
•Of all the fixed-pixel technologies, LCD has the biggest problem producing true blacks. Some light always passes through when the liquid crystals untwist, so the best black on most LCD panels is a very dark gray.
•Because of the way light passes through an LCD cell, direct-view LCDs usually have a narrower viewing angle than plasma TVs.
•Low-resolution LCDs exhibit distinct pixelation and screen-door effects when blown up to big screen sizes. For front projection, using a model with XGA (1,024 x 768) or higher resolution will reduce screen-door effects.
Where It's At
While direct-view LCD TVs are hugely popular in Japan and are just starting to turn heads here in the U.S., the initially high prices have slowed widespread adoption. Sharp's 37-inch LC-37HV4U LCD TV costs a cool $7,999, and its comparatively tiny 13-inch LC-13E1U lists for $899. Panasonic's and Sony's LCD rear-projection sets cost more than their CRT equivalents, with the 40-inch Panasonic PT-40LC12 currently listing for $3,499. But this September Sony plans to introduce a $2,500 42-inch model, which is more in step with CRT prices. As with DLP, the LCD front projectors offer the greatest variety-and the best deals. Products range from enhanced-definition TV (EDTV) models like the Panasonic PT-L200U ($1,999) to the HDTV-capable Sony VPL-VW12HT ($6,499). With several big TV players invested in LCD technology and both flat-panel and rear-projection models growing in popularity, LCD will be around for a long time.
What It Is
The least-familiar player at the fixed-pixel poker table, LCoS (liquid crystal on silicon) owes most of its technological heritage to LCD. But it outperforms LCD in many respects because it allows for smaller-size pixels that provide higher resolution and almost eliminate the screen-door effect. LCoS has tremendous potential for home theater, but at the moment it's only available in a handful of products.
How It Works
LCoS borrows from the technology for both LCD and DLP. Like LCD, each pixel in an LCoS display has liquid crystals that untwist to filter light, and-as the name indicates-these crystals are applied to a silicon chip instead of sandwiched between glass. As in DLP, light is reflected off the chip toward a screen. LCoS front projectors and rear-projection TVs can be designed with either a single chip, using a color wheel or prisms to separate the light, or three chips, one for each primary color.
•The only current rear-projection TV that uses LCoS-Toshiba's 57HLX82-demonstrates two major advantages that this technology has over both DLP and LCD: resolution and pixel spacing. The pixel count of current DLP and LCD displays max out at 1,280 x 720 and 1,366 x 768, respectively. But each of the three LCoS chips in the Toshiba set is packed with 1,920 x 1,080 pixels-enough to display all the detail in a 1080i-format HDTV broadcast. And because the pixels are spaced closer than those of the other projection technologies, the picture is smoother even when you look at it close up. It's difficult to judge the other performance aspects of LCoS from just one product, but the technology certainly looks good on paper.
•Can be expensive-the Toshiba 57HLX82 costs a staggering nine grand.
Where It's At
There were a number of LCoS front projectors and rear-projection TVs on display at this year's Consumer Electronics Show. JVC, for instance, showed one of the first front projectors, the DLA-SX21 ($9,995). And Philips plans to have four single-chip LCoS rear-projection sets in stores by this summer, starting at $3,499 for a 44-inch widescreen model. As with any emerging technology, some of the early products will probably have kinks to work out, but LCoS's resolution capability makes it a serious contender among fixed-pixel displays.