Rear projection TV (RPTV) became widely available in the 1980s as the first consumer-grade, affordable, big screen TV. RPTV is a type of television that uses technology which internally projects the viewed image from the rear of the unit to the backside of the display screen. There are four types of rear projection TV: Cathode Ray Tube (CRT), Digital Light Processing (DLP), Liquid Crystal on Silicon (LCoS), and Liquid Crystal Display (LCD). LCD technology is also used to make flat screen HDTVs, or non-rear projection models.
At a glance it’s easy to tell the difference between a rear projection TV and plasma or LCD flat panels. Flat panels are a few inches thick, easily mounted on a wall. RPTVs have electronics housed at the bottom rear of the set where units might measure some 14 inches (35.5cm) or more deep. The rear projection TV is, however, not as deep as traditional televisions and has a distinct advantage over them when it comes to sheer screen size.
The CRT RPTV has been largely replaced by microdisplays. Microdisplay DLP and LCD rear projection sets are market favorites, along with the newer LCoS HDTV, which is a hybrid of the other two technologies. If a wall mount is not required, the rear projection TV is a less expensive alternate to plasma and flat panel LCDs. Savings become exponential in sizes greater than 55-inches (140cm).
LCD rear projection is the oldest microdisplay design. DLP is newer but very close to LCD, though able to produce superior blacks for better contrast. Both traditionally use a white lamp and color wheel. On models that contain a single digital micromirror device (DMD) chip, some people report a fleeting “rainbow effect” in moving objects. Newer models that use an LED light instead of the white lamp don’t have this issue, nor do models with multiple DMD chips.
LCoS is the newest rear projection TV technology. It also goes by the names of D-ILA (Direct-drive Image Light Amplifier), and SXRD (Silicon X-tal Reflective Display). LCoS boasts a shallow physical profile, excellent blacks and grays that are arguably superior to DLP, and a separate DMD chip for each primary color, eliminating the potential rainbow effect.
Some flat panel LCD and plasma TVs have a “screen door” effect created by the individual pixels that make up the image, particularly if viewed too close. This can also be noticeable if an inadequate internal converter does a poor job of displaying a broadcast signal that is different from the native resolution of the set. Rear projection TV produces a smooth picture precisely because the image is projected on to the screen.
Rear projection TV requires lamp replacement every 3,000 hours or so, but unlike the backlight on flat panel LCDs, these lamps are comparatively inexpensive and user installable. If you are looking for an affordable large screen HDTV of 50 inches (127cm) or greater, a rear projection TV might just fit the bill.
