TV Buying Guide, by Alan Lofft -
Although the transistor was invented 50 years ago and most technology (from DVD players to cell phones to stereos) is "solid-state," its still a shock to realize that most of us continue to use a retro vacuum-tube entertainment device thats 75 years old--the cathode-ray tube (CRT) television set. Yes, that 28-inch or 36-inch "picture tube" that we stare at for too many hours a day is just a big, heavy glass vacuum tube with a flat face covered with groups of red, green and blue phosphors that glow whenever a scanning electron beam hits them. The beam traces out the same color image that a camera scans in the TV studio hundreds of miles away.
Invented in the 1930s, the CRT "direct-view" TV set
represents, in the parlance of the engineer, a
"mature" technology, which means its been developed
and refined over the past half-century to a level
that is impressive, affordable, and as good as CRT
can likely get. Admittedly, that clumsy, heavy
behemoth with the glass tube isnt "cool," but
properly adjusted, a conventional TV can still yield
picture quality that ranks with the best.
Even though we drool over those sexy, new thin flat-panel displays, conventional TV is still the most familiar and affordable. Heres a rundown on what to look for in the dependable conventional TV, either direct-view or rear-projection. To compute screen size, figure that to enjoy maximum clarity from a conventional TV, you should sit no closer than roughly three times the diagonal screen measurement of the set. So a 36-inch TV screen should not be viewed closer than 9 feet.
Conventional CRT TV sets
If you arent interested in High Definition TV or that new 16:9 "widescreen" picture shape (the aspect ratio of normal TV is 4:3), you can get a simple analog set and save a lot of money. The transition to HDTV is still moving slowly, and probably wont be complete for another five or 7 years. A conventional analog CRT set will still let you enjoy superb picture quality from a DVD player, but it wont display an HDTV image, nor will it show the film-like images possible from a DVD player with "progressive-scan" outputs, which eliminate visible scanning lines. To get that film-like image, you have to move up to a digital TV thats HDTV-capable, and if you want the 16:9 widescreen picture tube, the set will run you a couple of grand or more. But old or not, CRT sets can deliver stunning high-definition images. Maximum screen size is limited to about 40 inches, and if you plan to pull in HDTV signals over the air, youll need the accessory HDTV tuner, which runs an extra $500 to $1,000. Most digital cable boxes and small dish satellite tuners have the option of HDTV reception (with an upgraded dish).
Big-screen CRT sets use rear-projection (RPTV)-- actually three separate CRT guns for red, green and blue that overlap on the screen and must be precisely "converged," or aligned, from time to time (otherwise youll get color fringes around objects and faces). However, many new RPTV sets have auto-convergence circuits that align the three color guns in seconds, so what used to be a chore is accomplished with a few button-pushes. Rear-projection CRT sets still look their best in dimly lit or darkened rooms, although new RPTVs are remarkably bright. Here again you have the choice between the "old-fashioned" 4:3 screen shape or the HDTV 16:9 widescreen standard. Screen size and HDTV compatibility are the biggest price determinants here, but smaller HDTV-ready widescreen sets between 42 and 47 inches are about $2,000 and up. All HDTV sets have "line-doubling" circuits that receive any conventional non-HDTV signal and convert it to an image free of scanning lines. If youre hungering for high-def TV and you have a budget to consider, rear-projection CRT sets are the least expensive route to true HDTV.
Talked about for decades as the Next Big Thing, the proverbial flat-panel wall-mountable television display only a few inches thick has officially arrived, and now there is a group of new TV display technologies to choose from, all with improvements and some disadvantages. Herewith, a condensed guide to the new displays.
Plasma flat-panel display
the coolest TV around--its 3 to 5 inches thick and
from 32 inches to 60 inches in diagonal screen
size--the flat plasma panel uses a transparent
electrode behind a glass sandwich that encases
gas-filled cells coated with red, green and blue
phosphors (a second electrode is behind the
phosphors). The electrodes excite the gas, which
then stimulates the red, green and blue phosphors to
glow in the appropriate colors. Plasma panels
are so bright you can view them in a well-lighted
room, and they remain clear and bright over a wide
viewing angle. (By the way, since "pixel" may arise
in this discussion, a pixel is a "picture element"
that comprises a three-phosphor group) .
Downsides? Plasma panels still dont produce true blacks (theyre more gray than black), theyre subject to burn-in if youre not careful (an image permanently imprinted on the screen), and theyre expensive -- from $3,000US for a 42-inch panel enhanced-definition (EDTV) unit to $7,000 for the same screen size in a high-definition-capable panel. If you want a bigger screen, look at your bank account--a high-definition (HDTV) plasma panel 50 inches or larger will be $10,000US and up. Prices are expected to fall by about 1/3 every two years.
LCD flat-panel display
The liquid-crystal display (LCD) has been around for more than 20 years. If youve seen a laptop computer, youre familiar with an LCD flat panel. It uses an array of thin-film transistors (TFT) that power liquid-crystal-filled red, green and blue cells (again, each making up one pixel) in a glass sandwich. LCD panels have to have a light source to operate. When the transistors supply voltage, the liquid crystals untwist, allowing varying amounts of light to shine through them. As such theyre also easily adapted to a projector, where a bright lamp is focused through the LCD chip. LCD flat panels arent nearly as popular as plasma displays, and screen size is limited to about 37 inches, with prices into the $8,000US range. LCD projectors can be very bright and are capable of very accurate color rendition as well as HDTV resolution, but prices are high, into the $6,000 range or more. They also have the most trouble producing a true black, because whether in a flat-panel or projector, light always has to pass through the LCD chip. (Unlike a plasma display, the LCD panel doesnt originate light.) And as youve likely noticed with laptop computer displays, they arent viewable over as wide an angle. If low in resolution or clarity, LCD images can exhibit a "screen-door" effect, where each pixel becomes visible. But like DLP projectors (see below) LCD models are quite compact and lightweight, often 10 pounds or less.
DLP rear- and front-projection TV
Apart from the flat-panel plasma displays, digital light processing (DLP) chips are the newest and most talked about TV technologies. At the heart of all DLP devices is a 16:9 digital micromirror chip made by Texas Instruments. A high-intensity bulb is focused with a lens towards the DLP chip, whose surface is covered with nearly a million tiny pivoting mirrors that reflect light from the bulb onto a screen. Color is derived by filtering the light through a color wheel. The DLP chip is a huge advantage in a rear-projection set because the set can be made relatively thin (about 16 inches) and lightweight (75 lbs.) compared to cumbersome CRT sets. DLP rear-projection sets can be very bright with excellent high-definition clarity and although they are more expensive (about $4,500US for a 50-inch screen), they arent nearly as costly as high-def plasma panels or LCD. Used in a front projector, DLP is remarkably compact (the size and weight of a slide projector) and capable of quite bright, contrasty images with blacks that are better than plasma or LCD-based displays, almost as good as CRT blacks. And because the mirrors in the chip are integral to it, DLP projectors dont have convergence problems, nor are they subject to burn-in of images like plasma panels. DLP is still an emerging technology and some images can be subject to a "rainbow effect" if you glance quickly at the screen (Ive never seen it, but some critics comment on it). Many DLP front projectors range in price from as little as $1,500US to $6,000, depending on the projectors' HDTV capabilities. DLP technology also requires regular maintenance. Bulb life is about 2,000 hours (depending on your projector) and the bulbs cost about $450. For an affordable compact device free of convergence adjustments, DLP may well be the future of front and rear TV projection.