You know you want a flat TV, but you may not know whether a plasma or an LCD is best for you. Here's what you should consider before buying.

Recently, a friend sent me the following e-mail:

Random question, oh tech guru: I'm looking for a new TV, what are your thoughts on plasma vs. LCD? Moved to a loft, so I can get a decent-size "tube", but don't want to go broke. Also, looking at a 20-inch Sharp Aquos for the bedroom. Right way to go? Again, your thoughts.

The question wasn't as random as he supposed; I've been receiving similar queries from other friends and readers regularly for the past month. The great marketing machines of Philips, Sony, and Samsung have combined with electrical retailers to work everybody into a flat-panel frenzy -- even people who say they don't watch TV. The only problem, of course, is that there happen to be two kinds of flat panels, and both have their pluses and minuses. With that in mind, I've put together a quick rundown of what you should know before going the plasma or LCD route, along with a few pointers.

1. Price-to-size ratio
While neither LCD nor plasma TVs are a bargain, on a price-per-square-inch basis, plasmas currently have the edge. Look at it this way: technically, a 42-inch plasma gives you almost twice as much screen real estate as a 30-inch LCD panel, but they both go for about AU$3,000 [updated 07.03.06]. By 2006, you may see 42-inch LCDs hitting that price, but larger versions (50 inches or more) won't cost the same as their plasma equivalents for a while.

The reason my friend is looking at a 20-inch Sharp for his bedroom is that prices for smaller LCD panels are dropping the fastest, with a 20-incher coming in at a little more than AU$1,500. Plasmas aren't available in that size; 32 inches is their lower limit. Just remember that a 20-inch screen is pretty small, and you'll have to sit rather close to it. It may be fine for viewing sitcoms in bed, but it's obviously less than ideal for enjoying movies. And a 17-inch model should be reserved for use as a kitchen television or a computer monitor in a home office; while you work, you can watch TV in a little picture-in-picture box in a corner of the display.

Bottom line: 22-inch LCDs and 42-inch plasmas offer the greatest value among bedroom sets, and your best bet for the living room is a 42-inch or larger plasma.

2. Performance
A general rule of thumb is that plasmas deliver better home-theater performance than LCDs. Our video guru, Senior Associate Editor David Katzmaier, says that the difference is due mostly to the fact that LCD TVs typically can't display black as well as plasmas; it ends up closer to dark gray. That shortcoming decreases the amount of detail you can see in the shadows and ultimately leaves the picture looking -- as videophiles would say -- less three-dimensional.

The picture quality of both LCD and plasma panels is improving each year, but it can vary significantly from manufacturer to manufacturer. But if you're buying a smaller LCD (26 inches or less) for the kitchen or the bedroom, don't agonize too much over performance.

3. Life span
Life span, the number of viewing hours a television provides before dimming to half brightness, is one of the biggest advantages LCD has over plasma. Though the numbers vary among the different brands, plasma displays generally offer around 20,000 hours, while LCD sets last for up to 50,000 hours.

4. Burning issues
One of plasma technology's known issues is something called burn-in. It happens when your television shows a still image or an icon for so long that its "ghost" remains on the screen. For example, if a stock ticker or a news crawl continuously runs along the bottom of your display, that strip may be burned into your set. The same applies to watching an excessive amount of standard TV (4:3) on a wide-screen (16:9) model; the vertical bars to either side of the picture could become permanent. Manufacturers have taken steps to prevent burn-in, building in screensavers and other technologies. And you can virtually eliminate the danger by not leaving still images on the screen and reducing your contrast setting to 50 percent or less.

To their credit, LCDs don't suffer from burn-in, nor do they have troubles at high altitudes, where the air-pressure differential causes plasmas to emit an irritating buzzing sound. So, if you live at the top of a mountain, we don't recommend that you get a plasma, though some manufacturers are selling special sets that they claim are immune to the problem.

5. Viewing HDTV
Most plasmas and LCDs can display a high-def signal. However, you'll need a model with a resolution of at least 1,280 x 720 to enjoy full HDTV once it becomes available in the Australian market. Most 50-inch plasmas and nearly all 26-inch and larger LCDs offer this resolution. Very few 42-inch plasmas do, but when you're watching HD feeds on a lower-resolution television of that size or smaller, you'll have to sit very close to notice much of a difference between true HD and what you're seeing. Take, for example, Panasonic's TH-42PA20U, which is arguably the best 42-inch plasma we've seen to date in its price range. Even though the set provides only EDTV resolution (852 x 480), HDTV looks really good on it.

6. Computers and video games
Most plasma and LCD TVs can double as computer monitors; many even offer a DVI port for optimal video quality. They'll also hook up to a game console without any problems. So which technology is better for these purposes? From a performance standpoint, it's hard to pick a winner, but because of plasma's burn-in risk, LCD is the safer choice for computer work and gaming.