By: Alan Lofft, AxiomAudio
Invented in the 1930s, the CRT "direct-view" TV set represents, in the parlance of the engineer, a "mature" technology, which means it's 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 isn't "cool," but properly adjusted, a conventional TV can still yield picture quality that ranks with the best.
However, the US Federal Communications Commission (FCC) has decreed that by 2009, all TV broadcasters in the US must convert to digital broadcasts and turn off their analog transmitters. Your existing older CRT TV set will not receive those digital broadcasts without a special set-top adaptor. So if you've been thinking of replacing an aging CRT analog TV, with one of the newer digital TV displays--either Standard Definition or High Definition, then now is the time to do it, as prices for flat-panel plasma, LCD, and DLP rear-projection sets have fallen significantly.
But though we drool over those sexy, new thin flat-panel displays, conventional TV sets are still the most familiar and affordable. Here's a rundown on what to look for in the dependable conventional TV--whether analog or digital, 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 aren't 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 won't be complete for another 3 to 5 years. A conventional analog CRT set will still let you enjoy superb picture quality from a DVD player, but it won't 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 that's 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, digital 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, you'll need an HDTV with a built-in HDTV tuner. 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 you'll 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 digital CRT widescreen sets between 42 and 47 inches are about $1500 or less. 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 you're hungering for high-def TV and you have a budget to consider, rear-projection digital 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 
Unquestionably the coolest TV around--it's 3 to 5 inches thick and from 42 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. The best recent plasma sets benefit from excellent blacks and contrast, unlike some plasmas of a few years ago. (By the way, since "pixel" may arise in this discussion, a pixel is a "picture element" that comprises a three-phosphor group) .
Downsides? They use a lot of power, run fairly warm and are subject to burn-in if you're not careful (an image permanently imprinted on the screen). And although prices have dropped dramatically in the past two years, they're still fairly pricey--about $2,700US for a 42-inch HDTV plasma panel. If you want a bigger screen, look at your bank account.
LCD flat-panel display 
The liquid-crystal display (LCD) has been around for more than 20 years. If you've seen a laptop computer, you're 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 they're also easily adapted to a projector, where a bright lamp is focused through the LCD chip. LCD flat panels aren't as popular as plasma displays, in part because maximum screen size is limited to about 37 inches.
LCD flat panels as well as front and rear projectors can be very bright and are capable of very accurate color rendition and HDTV resolution. New models have much improved blacks and contrast., but LCD still has 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 doesn't originate light.) And as you've likely noticed with laptop computer displays, they aren't 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 front projectors (see below) LCD front projector 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. Like plasmas, they have come down in price, so you can get a 50-inch DLP rear-projection HDTV for $2200 or less. And they are less expensive than large plasma panels in big screen sizes. 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 the equal of plasma and better than LCD-based displays. And because the mirrors in the chip are integral to it, DLP projectors don't 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 effects" (flashes of bright colors around bright objects in a dim scene) if you glance quickly at the screen. Only a tiny minority of viewers are sensitive to it, but it's prudent to always check to see if you are someone who sees them. DLP front projectors range in price from as little as $1,100 to $10,000, depending on the projectors' HDTV capabilities, but excellent HDTV DLP front projectors now sell for $2,000 to $3,000US. DLP projector technology also requires regular maintenance, as do LCD projectors. Bulb life is about 2,000 to 8,000 hours (depending on the projector type; rear projector bulbs last longer) and the bulbs cost about $250 to $450. For an affordable compact HDTV device free of convergence adjustments, DLP and LCD front or rear-projectors are excellent choices. Variations on LCD technology, called LCoS (Liquid Crystal on Silicon) and DiLa are also very good.