Rear-projection TVs: CRT, DLP, LCD, and LCoS

Thinking of going big? Rear-projection HDTVs still offer the biggest screen for your buck, although falling prices among big-screen plasmas--58 inches and up--are forcing RPTV makers cut prices on their own. It's pretty obvious, in fact, that eventually RPTVs will go the way of the dodo as flat-panel HDTVs take over completely, but we're still years away from that. Rear-projection sets start at a mere 37 inches (diagonal), but the most popular models are 55 inches and larger. 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.

CRT

	Upside:		Downside:		Forecast:
	Relatively inexpensive.		Deep cabinets; need periodic maintenance; not ideal for bright rooms; narrow viewing angle; softer image than microdisplays; most cannot display computer signals.		These dinosaurs are quickly being phased out in favor of lighter, lamp-driven microdisplays, and their demise is clearly in sight.

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 they require careful setup and regular convergence adjustments to achieve sharp focus and maintain alignment of the red, green, and blue CRTs.

Low prices will keep CRT-based big-screen TVs in the game for another year or two, and videophiles may indeed point out that the best examples of this technology 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. Truly good-quality CRT-based big-screens are basically nonexistent now, however, and the product category as a whole is destined to die off sooner rather than later.

Microdisplays

A new generation of rear-projection televisions has effectively succeeded CRT-based RPTVs. These sets are called microdisplays because they're based on one or more microchips that contain thousands or millions of pixels. DLP, LCD, and LCoS are all competing types of chips. Every current microdisplay rear-projection TV contains a lamp that bounces light off of (DLP and LCoS) or through (LCD) its chip and onto the 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 more, 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 lamps take from 20 seconds to a minute to warm up and cool down. During the warm-up phase, the image is either dim or completely dark.
• The TVs are lighter and slimmer than CRTs, and you almost always need a stand to get them at eye level.
• Most can display computer sources, as well as high-definition 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 viewable 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, LG		JVC (HD-ILA), Sony (SXRD), Brillian
	Main picture-quality advantage(s)		Good pixel fill and uniformity; deep blacks in better models		Lack of rainbow effect		Excellent pixel fill; lack of rainbow effect; deep blacks in better models; 1080p chips have all 1,920x1,080 pixels
	Main picture-quality disadvantage(s)		Rainbow effect; low-level noise; wobulated resolution on many chips		Black level; screen door effect; uniformity		Uniformity
	Pervasive myth		Causes headaches		Degrades over time faster than other microdisplays		Subject to burn-in

DLP

	Upside:		Downside:		Principal brands:		Forecast:
	Very good black-level performance on the best models; excellent uniformity; wide selection of brands and price points.		Rainbow effects; some low-level video noise; currently no nonwobulated 1080p models.		Samsung, Toshiba, Mitsubishi, Panasonic, LG, RCA		DLP is only getting cheaper and more popular, and the best examples deliver excellent image quality.

DLP was developed by Texas Instruments, and the company sells many types of DLP chips to numerous traditional and not-so-traditional TV makers, making DLP the most widespread and popular microdisplay technology.

A tremendous range of DLP-based sets are available today, and their image quality varies greatly according to price and manufacturer. Entry-level models, among the least expensive microdisplays you can buy, generally have 720p native resolution (1,280x720). Step-up models have 1080p resolution (1,920x1,080), which can deliver sharper images with 1080i HD and computer sources (more info on 1080p).

Both 1080p and some 720p DLP televisions use a technique called "wobulation" to achieve their stated native resolutions. With wobulation, which Samsung calls SmoothPicture, the DLP chips have half as many physical pixels (a 1080p chip has 960x1,080 pixels). A tiny mirror or lens moves rapidly back and forth to alternately create the first and second halves of the image and achieve 1,920x1,080 resolution. Wobulation can produce good results, and on some 1080p TVs, it can technically deliver all 1,920 lines of horizontal resolution; on other sets, it makes the image look softer. As usual, performance varies from model to model.

One potential problem with DLP sets is known as the rainbow effect. Some people can see brief streaks of color on these TVs, especially in images with black fields and some bright features (such as a spaceship). 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 only see them 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.

New DLP technologies address a few of these issues. Samsung sells HDTVs, such as the HL-S5679W, that use LEDs instead of the traditional bulb. In addition to lasting 20,000 hours, the LEDs eliminate the rainbow effect, although as noted in our review, the TV had some uniformity issues. The company announced new LED-powered DLPs for 2007 as well, which may address these issues. Mitsubishi, for its part, demonstrated a laser-powered DLP HDTV last year that hits the market later in 2007.

LCD

	Upside:		Downside:		Principal brands:		Forecast:
	No rainbow effect.		Blacks not as deep as the best LCoS or DLP sets; some uniformity issues; visible screen-door effect.		Sony, Hitachi, Panasonic, LG		LCD will continue to challenge DLP among entry-level sets, and the appearance of 1080p versions could extend its appeal to higher-end buyers.

Though less popular than DLP models, LCD-based rear-projection sets should continue to do well as long as Sony stays in the game. The company has developed a step-up chip, however, which it calls SXRD (see below) and puts in its higher-end rear-projection HDTVs. We did not review any LCD-based rear-projection HDTVs in 2006, but this year we're excited to check out Sony's new models, which include some of the first 1080p LCD-based rear-projectors and slimmer cabinet designs

Judging from previous models we've tested, the best DLP and LCoS sets still hold the lead in producing the deepest blacks, but LCD chips have made serious improvements. 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 and LCoS have an image-quality advantage is something called the screen-door effect. If you sit close to an LCD--at least the 720p versions we reviewed in the past--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. We expect the new 1080p LCDs to have a much less noticeable screen door effect, if they have it at all.

LCD and LCoS also generally have more white-field uniformity issues than DLP. With expansive flat fields, such as the ice in a hockey rink, some LCD and LCoS sets introduce slight discoloration into some areas of the screen. This effect varies widely from model to model, but DLP sets are generally immune.

LCD's big advantage over DLP--one that it shares with LCoS--is its 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. Though this is essentially true, it has little impact on a product's real-world 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.

LCoS

	Upside:		Downside:		Principal brands:		Forecast:
	Excellent black levels on the best models; great interpixel fill; no rainbow effect; true 1,920x1,080-pixel chips on 1080p models.		Some uniformity issues.		JVC, Sony, Brillian		As long as Sony sticks with SXRD, LCoS will continue to be regarded as a worthy competitor to the best DLP HDTVs.

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 market, which has since proven untrue. Today, JVC and Sony are the only major LCoS makers, and each company's HDTVs have performed very well in our tests. It remains to be seen whether other manufacturers will jump on the LCoS bandwagon, although chipmaker Brillian has an expensive LCoS line of its own.

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 and employing yet another acronym: HD-ILA. JVC's HD-ILA expanded in each succeeding year, including well-performing models like 2006's HD-56FN97. We're excited to check out the new sets, especially the extra-slim HD-S998 series.

Sony (SXRD): Much like JVC, Sony rebranded its LCoS chip, choosing to call it SXRD (Silicon X-tal Reflective Display or Silicon Crystal Reflective Display). In 2006 we reviewed two models, the KDS-60A2000 and the step-up KDS-60XBR2, that delivered excellent picture quality. Despite their high prices, Sony's SXRD sets remain extremely popular. The company has announced that its entry-level 2007 SXRD sets, the KDS-A2020 series, is basically unchanged from last year's A2000, so we eagerly await details on the 2007 XBR models.

Source: http://www.cnet.com/4520-7874_1-5108443-3.html?tag=arw