These big-screen sets are losing the bulk they were known for.

New rear-projection TVs are microdisplay sets that use miniature technology, digital-light processing (DLP), to create large images on screens measuring up to six feet or more diagonally.

These TVs are slimmer and lighter than bulky projection sets using cathode-ray tube (CRT) technology, which used to be the norm. (CRT-based projection sets are no longer available, nor are recent models using liquid-crystal display (LCD) or liquid crystal on silicon (LCoS) technology.) Overall, sales of rear-projection sets have been shrinking as flat panels have become larger and lower-priced.

Mitsubishi and Samsung are the only manufacturers of rear-projection TV. Sony, Hitachi, Philips, and Toshiba have all left the category.

Most sets measure about 50 inches diagonally and larger; models with 50- to 59-inch screens are the best sellers. The largest TVs have screens measuring 73 inches or more.

Virtually all rear-projection TVs now on the market are digital HD sets. Most are 1080p models with 1920x1080 resolution, offering the potential to display all 1,080 lines in the most common HD format, called 1080i. The improvement is most noticeable on screens 50 inches and up, which includes most rear-projection TVs.

Most microdisplays are less obtrusive. Typically they are 15 to 20 inches deep, and some “slim-line” models are now just 10 to 12 inches deep.

A stand for a microdisplay television is recommended; a matching stand, sold separately, is usually available.

Since March 2007, all new TVs sold in the U.S. must include a digital tuner. This enables them to receive free digital TV, including high-def programming, via an over-the-air antenna.

Rear-projection TVs have the features that are now standard on higher-priced TVs. Like virtually all new HDTVs, rear-projection sets have 16:9 wide screens. Because some TV content is still formatted for a squarish 4:3 screen, HDTV sets have stretch and zoom modes that expand or compress an image to better fill the screen. This helps to reduce the dark bands that can appear on the sides or top and bottom of images not formatted for a wide screen. (The picture might be distorted or cut off in the process.)

A film-mode feature improves the appearance of movies converted from film to video, including the majority of cinematic movies on DVD and some movies broadcast on cable, via satellite, or over the air. This feature is also called 3:2 pull-down, motion compensation, or brand-specific names such as CineMotion and Film Mode. It helps compensate for the difference in frame rates between film (24 frames per second) and video (30 frames per second), so moving images look less jerky and jagged around the edges.

When watching DVDs on a progressive-scan player, try enabling this feature first on the DVD player and then on the TV, and use whichever makes the images look smoother.

All TVs have menus with settings that enable you to adjust the video, audio, and more. With more sources for video available all the time, it’s handy to have a feature that allows you to customize settings for each input, such as the one you routinely use for your cable box or the DVD player. For example, you might want sharpness set to its lowest level when watching high-quality DVDs routed through the HDMI input, but a higher sharpness setting to improve the look of standard-definition programs coming in through the component-video input.

Picture-in-picture lets you watch two TV channels at once, one in a small box, the other a full-screen image. It’s useful, say, if you want to browse the onscreen guide while keeping an eye on the program you’re watching, or keep track of a sports event while a program is playing. A single-tuner TV requires another device with a tuner, such as a VCR or cable box, to display two programs at once; dual-tuner models can display two programs simultaneously on their own.

CableCard slots on a small number of HDTVs let you use a card, provided by the cable company for a small rental fee, instead of a cable box. When the card is inserted, the TV can receive scrambled digital cable content, including HD programming. This eliminates the need for an extra piece of equipment and cables, but there is a downside. Current CableCards are one-way, so they don’t provide an interactive program guide, video-on-demand, or pay-per-view ordering. But some TVs have a built-in program guide, such as TV Guide On Screen, that displays eight days of programming in a searchable, interactive format.

One of the most important points to consider with any TV is the number and type of inputs it has. There are several types that can handle high-def signals: HDMI, DVI, component-video, and RF. HDMI inputs provide a digital connection to devices such as DVD players, digital-cable boxes, and satellite receivers. HDMI carries audio and video on one cable. DVI carries only video and must be used with separate audio cables; these are much less common than HDMI. Component-video inputs are analog; they use red, green, and blue RCA jacks to carry the video and must be used with separate audio cables. The RF input can be used to get digital signals, including HD, from an off-air antenna.

Other useful analog inputs on new TVs include composite-video and S-video, which can connect equipment such as VCRs and DVD players. Inputs on the front or side of a set are more easily accessible than those in the rear, but you’ll be able to see the cables plugged into those jacks.

Some projection sets have a memory-card slot. That enables you to view still photos or videos from a digital camera. You can connect a camera or camcorder directly to the TV if it has a PictBridge, USB, or IEEE 1394/Firewire input. A VGA input lets a TV accept signals from virtually any computer; DVI inputs are compatible mostly with newer midrange computers. A headphone jack is handy if you want to listen to TV without disturbing others. An illuminated remote is handy in a dim setting. Backlit keys are preferred because glow-in-the-dark buttons often fade quickly.

Consider space before settling on screen size. You might be tempted by the biggest screens, which can span 73 inches or more, but take measurements first. Figure out how much floor space you can actually spare, and plan to view the TV from about 7 to 9 feet away for optimal picture quality.

Consider reliability. Our surveys have shown that rear-projection microdisplays have been more repair-prone than flat-panel and tube TVs. The overall repair rate for seven major brands of DLP and LCD-based projection sets covered in our survey was 18 percent (for sets purchased between 2004 and 2007). Toshiba and RCA DLP sets were most repair-prone. Hitachi LCD-based sets were more repair-prone than Sony and Panasonic. We don’t have enough historical data on LCoS sets for a repair chart by brand, but we have enough data to see that Sony sets of this type have been more reliable than JVC sets. Despite the comparatively high repair rate, most rear-projection sets have been trouble-free in their first few years, and many of the reported repairs were covered by a standard warranty. So an extended warranty still seems like a poor investment for most consumers.

Focus on picture quality. The best rear-projection sets can deliver excellent picture quality with HD content, DVDs, and regular TV programs. Within the microdisplay category, we haven’t found that any one projection technology was consistently better than another. There are a growing number of sets that offer 1080p resolution, and some of those have been among our top-rated performers.

Check the viewing angle. Some new models do a better job than older sets at maintaining their image quality when viewed from off-center, a must if the TV will be watched by several people at once. Before buying one, see how the picture looks if you step off to the side or move up and down. With some, you’ll see a dimmer, somewhat washed-out image as your viewing position angles away, particularly in a vertical direction.

Consider logistics. Rear-projection sets stand on the floor or rest on a stand, so installation is easier than for front-projection systems or wall-mounted plasma TVs. Still, rear-projection sets are large and can be difficult to transport and set up, so consider having the set delivered.

Consider bulb life. Most rear-projection microdisplays use a backlight with a claimed life expectancy of about 5,000 hours. You’ll hit that point in about four years if the TV is turned on for four hours a day.

When a bulb burns out, you won’t see any picture; most sets have an alert of some type to indicate you’re nearing the end of the rated life, so you won’t be caught by surprise. Replacement bulbs cost from $200 to $400.

Replacement isn’t that difficult, no harder than replacing a car’s headlight, so you can do it yourself as long as you’re comfortable wielding a screwdriver. This simple bulb replacement procedure is explained in the manual. You can also pay for professional installation, which can add another $200 or so to the cost of replacement.

A few new models have longer-life bulbs; one we’ve seen was rated at five years. Others, such as Samsung, are using LED illumination instead, and one company, Mitsubishi, is expected to introduce a model lit by lasers later this year. These types of backlights can expand the range of colors the set can display and eliminate the need to replace the bulb during the life of the set.