For Shoppers, a TV Guide By ROY FURCHGOTT

For Shoppers, a TV Guide By ROY FURCHGOTT

WHEN most people buy a television, they measure the wall where they want to put it and then pick the largest screen that will fit. That is exactly the right way to buy a big TV, but it misses the point if you want the right TV.

The good news is that picture quality has improved radically in the last five years, even as prices have plummeted. The bad news: there are a bewildering number of specifications and features to consider. Many of them will matter only to hard-core videophiles, but some are critical to everyone.

One of the basic features is the type of set. Although projection and tube televisions are still available, most people choose either a plasma set or one of the two types of LCD televisions.

Most of the professional installers I consulted prefer plasma televisions. And if you want a flat-screen model that is wider than 50 inches, there are few other choices.

The installers say that plasma sets have the smoothest motion, the truest blacks — more on that later — and are more easily watched from side angles than the LCD variety. Moreover, “plasma is generally cheaper,” said Shawn G. DuBravac, the director of research for the Consumer Electronics Association.

But plasmas also use more energy than LCD sets — making them more expensive to run — and LCD sets can work better in bright rooms because they have higher bright settings than plasmas. “The electricity cost of powering the TV, even for the largest models, amounts to less than $2 a week,” Mr. DuBravac said. “That’s if you watch TV five hours a day, seven days a week.” The cost may not bother every customer.

There are also big differences among LCD sets. One technical distinction is that older LCD sets are backlighted by a fluorescent lamp, while the newer ones, called “LED LCDs,” are lighted by hundreds of LEDs. These models can be brighter and have a higher contrast than their older cousins, and they are thinner, too — less than an inch compared with three or so inches.

LED screens tend to have better black levels than the older LCDs. The reason: Regular LCD sets create black by closing off a crystal, but light can still leak through — think of a cloth draped over a lamp. The LED variety, with its hundreds of individual lamps, can effectively turn off the light source — that is, click off the light rather than drape a cloth over it. But even that is not perfect. Although there are hundreds of lamps, there are millions of the pixels that make up the set’s picture, so a “black” area will still have a few lighted pixels. In plasma sets, however, the cells that make up the picture are lighted individually, making its blacks better still.

Resolution — the sharpness of the picture — is a second major factor for buyers. A few years ago, there was a complex variety of choices, but there are now just two — 720p or 1080p. (These terms refer to the number of lines on the screen, with anything higher than 720 considered high definition.)

Generally, 1080 offers finer resolution at a higher price, but that is not the end of the story because television broadcasts, DVDs and Blu-ray all enter the set at different resolutions. To make the number of lines from the source match the number of lines on the set, the television must use its computing power to scale the picture, and its ultimate quality will depend on how well the set’s computer and software do their jobs.

There is no measurement for computing power. You have to rely on your eyes at the store, and maybe on experts’ and owners’ reviews. In one case, though, the 1080 is inarguably better, and that is for Blu-ray discs. They have 1,080 lines of resolution, so they can match any television bearing the same measure. To get the most from Blu-ray, however, dig deep into the owner’s manual to make sure the television set accepts a “24p” signal, (look under “allowable” or “supported” input signals). If not, even with the 1,080 match, the set will need to do more processing to convert the signal properly.

What about 3-D televisions? One downside is that the number of 3-D programs and films is sharply limited. A 3-D set is also nearly double the cost of a comparable 2-D set, and that does not include the cost of 3-D glasses, which are weightier than the old cardboard versions and cost $100 to $300.

As with many television tech issues, there is yet another twist: because 3-D requires so much processing power, the sets tend to have excellent computer processing. That capability means better pictures — even for people who use the sets only for 2-D viewing.

Unfortunately, the televisions’ computers are complex, and appraising them is not easy. Be sure to pay attention to the refresh rate. That is the speed at which the set can put up new pictures, and it affects how fluidly images move on the screen.

Video purists prefer a refresh rate of 60 hertz because it is “true” — the same rate as that of broadcast television. But on either kind of LCD set, that slow a rate can blur the motion in sports broadcasts and action movies. (“Motion blurring is not an issue” on plasma TVs, said Bill Schindler, a television engineer and researcher.)

To minimize blurring on LCD sets, many people prefer a 120-hertz refresh rate. When broadcast television sends out its 60 pictures a second, a 120-hertz set must fill in twice as many frames, guessing what a picture between the two broadcast images would look like, and then creating it. Most sets can handle a 120 rate effectively — but a 240-hertz rate can mean problems.

“There is an awful lot of interpolation going on at these higher frame rates,” Mr. Schindler said. “In the case of 240 you have to make up three pictures” for every real one received.

Moreover, the more processing required, the greater the likelihood of “artifacts” — processing mistakes that show up on the screen. A classic artifact: spokes that “appear to be going backward” on a stagecoach in a Western, said Joe Kane, a video display consultant. “If the processing isn’t very good, they appear to be going backward even worse.”

More and more televisions can be linked to the Internet, but if you plan to buy one, keep two things in mind. First, apart from the set itself, the quality of what you get will depend on your Internet speed. That may mean one more thing to upgrade. Second, as you browse, realize that the sites and services available on a Web-enabled television may change after your purchase. If a film service — Hulu or Vudu, for example — becomes more widely used, a TV maker may add it to the menu of links available. The shifting array of features makes comparison shopping difficult.

“If something is popular,” said Mr. DuBravac of the Consumer Electronics Association, “it’s going to be developed for multiple devices.”

Finally, what about the size of the set — the feature that many people deem all-important? Buyers may think they know the proper size, said Sy Paulson, a manager at the Best Buy store at Union Square in Manhattan, but their calculations are frequently “hit or miss.”

The critical factor is the distance between the viewer and the set. The rule of thumb is to take that distance — say, 60 inches — and divide by three, and the result — 20 inches — is the ideal height of the screen. (Screen height is usually about half the screen’s diagonal measure.)

With high definition, the picture will look good even close up. But if you get too close, you risk whiplash just trying to follow the action.