March 2005
| Decoding projection-TV lingo CRT, LCD, DLP, LCoS--acronyms like these could have your head spinning when you go shopping for a rear-projection TV. The term for the category itself can be a puzzle. You might wonder why rear-projection sets are called that, given that there's no projector anywhere in sight. It's because the projector is inside the cabinet. An image is created within the set and projected onto the rear surface of the screen (hence the name “rear projection”). By contrast, direct-view sets (picture-tube TVs and flat-panel LCD and plasma displays) create images right on the screen, not internally. Various technologies are used to create the images on projection TVs. CRT. This type of projection TV contains three CRTs, or cathode ray tubes--one each for red, green, and blue--making the cabinet big and heavy. Three beams converge on the inside of the screen to form an image. You must periodically align the CRTs, using the TV's controls, to ensure a sharp image. All but the cheapest sets now have an automatic convergence feature that makes this a quick and easy process. Microdisplays. This is an industry term sometimes used to describe rear-projection sets using LCD (liquid-crystal display), DLP (digital light-processing), or LCoS (liquid-crystal on silicon) chips and a bright lamp to create images. This space-saving “light-engine” technology makes microdisplays slimmer and lighter than CRT-based sets. Most microdisplays are tabletop sets 15 to 20 inches deep that weigh about 100 pounds. CRTs are floor-standing sets 24 or more inches deep, and many weigh about 200 pounds. Here's a look at the three types of microdisplays. LCD. These TVs have three LCD panels inside. Don't confuse LCD-based rear-projection TVs with LCD flat panels, though. These big TVs are more than a foot deep. The best of the LCD-based projection sets we've tested displayed very good picture quality. None of these sets, however, were able to display the deep black levels of TVs using other technologies, and the contrast wasn't as good as we've seen on other types of TVs. Some older LCD projection sets can suffer from blurring during fast action sequences. DLP. These sets create images using a digital light-processing chip with millions of tiny mirrors. Rear-projection DLP sets have one chip and a rotating color wheel, which may cause occasional annoying flashes of color visible to some viewers--what's called the rainbow effect. Some front projectors have three chips; they don't have that problem. The best of the DLP projection sets we've tested displayed very good picture quality. LCoS. These sets share some attributes with LCD and DLP, using both tiny mirrors and liquid-crystal technology. The technology's rollout has been hampered by production problems and costs, prompting companies such as Intel and Philips to abandon their LCoS plans. Because LCoS sets have been slow to market, we've tested only two so far. Both had good picture quality. JVC has an LCoS variant that it calls HD-ILA, using Direct-drive Image Light Amplifier technology. |
