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Rear-projection TVs: CRT, DLP, LCD, and LCoS
(updated August 4, 2005)
Thinking of going big? Sure, you could buy an 80-inch plasma, but most people who want to maintain a good credit rating will opt for a rear-projection television (RPTV) instead. These sets start at about 42 inches diagonal, and the majority support the wide-screen, 16:9 aspect ratio and have built-in HDTV tuners. Their big screens hide two basic varieties of display technology: old-fashioned CRT tubes; and microdisplays that use DLP, LCD, or LCoS technology. Here's an introduction to the choices.
Upside: Relatively inexpensive; excellent black-level performance; still the best picture quality in a proper environment with proper setup.
Downside: Deep cabinets; need periodic maintenance; not ideal for bright rooms; narrow viewing angle; softer image than microdisplays; most cannot display computer signals
Forecast: These dinosaurs are quickly being phased out in favor of lighter, lamp-driven microdisplays, and their demise in clearly in sight.
Mitsubishi, producer of the WS-55315, still sells a full line of CRT-based RPTVs, but the popularity of these large sets is fading fast.
Tube-based RPTVs used to rule the big-screen roost, but unless you're really strapped for cash or willing to get professional calibration to achieve the best home-theater image quality, we recommend skipping the tube in favor of a microdisplay. Tubes are not as bright as microdisplays and require careful setup and regular convergence adjustments to achieve sharp focus and maintain alignment of the red, the green, and the blue CRTs.
Relatively low prices will keep CRT-based big screens in the game for another couple of years, and videophiles may indeed point out that they still provide superior image quality in many ways. They still have better black levels than any microdisplay; they generally have deep, well-saturated color; and they can achieve a sharp picture if adjusted properly. The image quality issues noted earlier, however, and especially their significant bulk, make these beasts destined to die off sooner rather than later.
Smaller box: Microdisplays are lighter, shorter, and thinner than CRT-based rear-projection HDTVs.
A new generation of rear-projection televisions is taking over floor space at the electronics store, and the trend shows no signs of slowing down. These sets are called microdisplays because they essentially consist of a lamp that bounces light off of or through a tiny pixel-filled microchip and onto a big screen. Below is a brief look at how microdisplays differ from standard televisions, as well as a cheat sheet to give you a quick grasp of the many abbreviations and terms in this category. More in-depth explanations of each technology follow.
- The lamps inside these sets, which cost $200 and up, must be replaced every 3,000 to 10,000 hours, depending on technology and conditions of use. You can replace most lamp assemblies yourself.
- The bulbs take from 20 seconds to a minute to warm up and cool down.
- The TVs are generally lighter and slimmer than CRTs, and you almost always need a stand to get them to eye level.
- Most can display computer as well as high-def and standard TV and usually look better when fed a digital (DVI, HDMI, or FireWire) rather than an analog connection.
- Unlike rear-projection CRT sets, all microdisplays can get quite bright without losing detail, so they're perfectly watchable in brightly lit rooms.
Microdisplay cheat sheet
| | DLP | LCD | LCoS |
| Full name | Digital Light Processing | Liquid Crystal Display | Liquid Crystal on Silicon |
| Chipsets, variations, and brandings | HD2, HD2+, HD3, xHD3 | 3-LCD, H-LCD | HD-ILA, SXRD |
| Principal brands | Texas Instruments (chip producer), Samsung, Toshiba, Mitsubishi, Panasonic, LG, RCA | Sony, Hitachi, Panasonic, Mitsubishi | JVC (HD-ILA), Sony (SXRD), Hitachi |
| Main picture quality advantage(s) | Black level; good pixel fill; uniformity | Lack of rainbow effect | Excellent pixel fill; lack of rainbow effect |
| Main picture quality disadvantage(s) | Rainbow effect; low-level noise | Black level; screen door effect; uniformity | Black level (see below); uniformity |
| Pervasive myth(s) | Causes headaches | Degrades over time faster than other microdisplays | Intel is producing LCoS televisions |
Upside: Good black-level performance; no maintenance required to preserve sharpness; often computer-capable; thin and light compared to CRT.
Downside: Expensive; some rainbow effects; video noise in dark areas; periodic lamp replacement required.
Principal brands: Samsung, Toshiba, Mitsubishi, Panasonic, LG, RCA
Forecast: DLP is only getting cheaper and more popular, although LCD will give it plenty of competition.
Samsung's pedestal-mounted HL-P5085W DLP TV shows off the possibilities of microdisplay design.
We've been talking about black levels a lot, so let's finish the discussion right here: Aside from CRT models (and possibly SXRD LCoS designs; see below), DLP sets currently provide the deepest blacks of any projection technology. Recent advancements in LCD have narrowed the gap considerably, but DLP still has a slight lead. Almost all DLP-based RPTVs use a 1,280x720-native resolution chip that shows every pixel of 720p HDTV, resulting in a very sharp picture with high-definition sources. A new generation of higher-resolution DLP displays is also hitting stores in 2005, offering 1,920x1,080 resolution that should be able to display every pixel of 1080i HDTV. These so-called 1080p DLPs cost quite a bit more than their 720p counterparts.
One potential problem with DLP sets is known as the rainbow effect. Some people can see brief streaks of color on these TVs, especially when moving their eyes across the screen. This is caused by the fact that the single DLP chip uses a color wheel to create red, green, and blue, and hence all colors. The occurrence of these rainbows has been significantly reduced with the advent of newer, faster color wheels, and most people who watch a DLP never see rainbows at all (and the few who do usually see them only occasionally). DLP HDTVs do introduce a bit more low-level video noise, which can look like tiny dancing pixels or motes in shadowy areas, than other microdisplay TVs.
Upside: No rainbow effect; no maintenance required to preserve sharpness; often computer-capable; thin and light compared to CRT.
Downside: Expensive; blacks not quite as deep as DLP; periodic lamp replacement required.
Principal brands: Sony, Hitachi, Panasonic, LG
Forecast: LCD has made some tremendous leaps in performance and will continue to challenge DLP as prices fall fast.
While DLP still holds the lead in producing the deepest blacks, LCD chips have made serious improvements recently, bringing their black-level performance to within striking distance of DLP. Translation: Unless you have them side by side, you probably won't be able to tell which of the two delivers the deepest blacks. Prices for similarly sized DLP and LCD TVs will likely remain close as big-brand behemoths face off and try to outdo one another.
Another area where DLP has an image-quality advantage is something called the screen-door effect. If you sit close to an LCD, you may notice a faint grid of pixels, much like a screen door, overlaid atop the image. You're seeing the space between the pixels, which is more visible on LCD than on the other two microdisplay technologies. It's generally not noticeable even on LCDs unless you sit closer than twice the diagonal measurement of the screen.
LCD's big advantage over DLP, and one that it shares with LCoS, is lack of the rainbow effect--a big deal if you see rainbows on DLP sets, and a moot point if you don't. Don't put too much stock in the slightly higher native resolution afforded by some LCD chips; in the big scheme of things, 1,386x788 doesn't provide much of a sharpness boost over 1,280x720. DLP makers have also claimed that the organic compounds in LCD chips degrade over time, while DLP chips do not. While this is essentially true, it has little impact on real-world product life span because LCD chips still last very long time under normal working conditions. While LCoS and DLP makers tout the "inorganic" nature of their chips, we don't consider that a major reason to choose one technology over another.
Upside: Excellent interpixel fill; no maintenance required to preserve sharpness; thin and light compared to CRT; more dependent on variants (below).
Downside: Periodic lamp replacement required; more dependent on variants (see below).
Principal brands: JVC, Sony, Hitachi
Forecast: LCoS is back from the dead, and two radically different variants prove the technology has plenty of staying power.
JVC's HD-52Z575 is the company's first attempt at an LCoS-based microdisplay RPTV.
LCoS has been through some trying times, and Philips, Toshiba, and Mitsubishi are among the heavy hitters that produced early-generation models, then decided to abandon the technology. Intel even floated a rumor that it would enter the LCoS stakes, which has since proven untrue. But in the second half of 2004, JVC and Sony introduced variations on LCoS chips, which each deserve their own explanations. And in the early part of 2005, Hitachi jumped on the LCoS bandwagon with its own 1080p LCoS lineup, due later in the year.
JVC (HD-ILA): JVC has been producing LCoS-based front projectors for years under the D-ILA (Direct-drive Image Light Amplifier) brand, and in 2004 the company proffered a line of rear-projection sets, exemplified by the HD-52Z575 (pictured) and employing yet another abbreviation: HD-ILA. They're priced very competitively with DLP and LCD sets and offer the same resolution (1,280x720) as well as the brightest picture and best interpixel fill we've seen on a projection TV. Unfortunately, black level wasn't as good as either LCD or DLP, and we ran into some other issues (see the review for more). JVC has announced 1080p HD-ILA televisions that will appear later in 2005.
Sony (SXRD): Unlike JVC, Sony decided to charge an arm and a leg for its LCoS variant, dubbed SXRD (Silicon X-tal Reflective Display or Silicon Crystal Reflective Display). Initially available only in the Qualia 004 front projector ($27,000) and Qualia 006 70-inch rear-projector ($13,000), the 1,920x1,080 SXRD chip looks to be an excellent candidate for the best microdisplay technology yet. Initial reports indicate that it delivers excellent black levels, a minimum of video noise, and numerous other refinements. We expect the company will officially announce lower-priced SXRD-based HDTVs by January 2006.
Hitachi: The third big-name player hasn't cooked up a fancy name for its LCoS-based lineup, and in terms of pricing, Hitachi's sets fall somewhere between those of JVC and Sony. Since these models won't be released until late 2005, we don't know much about them yet, but stay tuned.
 
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