CNET.com.au's quick guide to TV types

Once upon a time, when only direct view TVs were around, buying a new set used to be a whole lot less of a nerve-racking experience. Now, there are all sorts of questions. Do you go wide or not? Is LCD better than plasma? And how do I make sure I'm ready for digital and high definition TV?

If all the tech jargon has you confused, don't worry. Read our guide to the pros and cons of new, high-tech TVs, and you'll feel a whole lot more confident when you hit your local electronics store.

Direct-view is how industry insiders refer to any television that doesn't use projection technology. Most of them are the familiar tube TVs you see everywhere -- they're called tubes because the glass forms the business end of a cathode-ray tube (CRT). Direct-view tube TVs can be found in sizes up to 86 cm diagonal, and as their screen sizes increase, so does their heft and depth. Some of the biggies tip the scale at 88kg and require a minimum of two burly guys to lift it onto a stand. Because of size and weight issues, it doesn't pay for companies to make larger tube TVs; they simply aren't practical.

High-end tube TVs can give a great-looking picture. CRTs are still the kings of black level, a term used to describe the quality and the depth of black and other very dark colours. Direct-view tube sets look good from any angle, so the picture quality doesn't change depending on where you sit. These TVs can also be viewed in brightly lit rooms and last 5 to 10 years with only a minimal loss in picture quality.

Flat vs. curved screen: The traditional curved shape of the glass tube is giving way to completely flat glass. Sony introduced flat tubes first with its WEGA televisions, but now, just about every manufacturer sells some kind of flat-tube TV. Flat glass not only looks more high-tech, it collects less ambient light from the room and, therefore, helps to reduce glare. But it's a myth that flat tubes result in straighter lines; they can have the same geometry problems as their curved counterparts, especially near the corners and the edges of the screen.

Wide-screen 16:9 vs. standard-screen 4:3: For the strongest theatrical impact, the majority of movies are filmed in the wide-screen format, where the screen is much wider than it is tall. Regular televisions have used a narrow-screen, 4:3 aspect ratio, which refers to the width of the screen compared to its height. Newer TVs often have screens with a much wider ratio: 16 units of width for every 9 units of height, which translates to a 16:9 aspect ratio. Wide-screen, direct-view TVs cost quite a bit more than 4:3 models for the same amount of screen real estate, but they're great if you watch a lot of DVDs or digital television programming.

The biggest television-technology revolution in the last couple of years, flat-panel TVs will eventually replace tubes as the direct-view televisions of choice. The two major players in the flat-panel game are plasma and LCD, so we'll go over each type separately. Note: Almost all plasmas -- and many LCDs -- are digital TV-capable, meaning that they can accept a standard-definition or high-definition signal. However, many of these sets don't have enough pixels to display the full resolution of HD TV.

Twelve months ago you would have been hard pressed to find a plasma set under $10,000, but prices have been in free-fall this year, and new models have been pouring onto the market. You can now find an entry level 42" plasma at around the $5,000 mark. Still a sizeable chunk of cash compared to a direct view set, so plasma TVs are still seen as a "I wish I had that" toy.

If you can swallow the payments, however, you'll get a sexy, flat-panel TV with a picture that's nearly as good as that of a CRT. The word plasma refers to the gas trapped inside every pixel, which lights up when an electric charge is applied.

Despite significant advances, plasma panels still can't replicate the deep blacks that tubes can, and so don't look quite as good for home theatre in a darkened room. A handful of today's top-rated models come pretty close, though, and as the technology matures, we expect to see more plasmas with good black-level performance.

You may have heard that plasma has a couple of drawbacks. One such downside is called burn-in, which occurs when an image -- such as stock ticker or a network logo -- gets etched permanently onto the screen because it sits in one place too long. However, if you take a couple of preventive steps, the risk for burn-in can be greatly diminished. As long as the contrast control is kept to a reasonable level (we recommend 50 per cent or less), and you avoid showing static images on the screen for hours at a time (gamers take note), a plasma screen should not burn in. Newer panels also have burn-in-reduction features that further reduce this possibility.

The life span of a plasma TV is probably not as good as that of a CRT, but these panels still last quite a while. The typical plasma lasts 20,000 to 30,000 hours, which equates to at least two years, three months of 24/7 usage, before the panel fades to half brightness.

Think of flat-panel LCDs as plasma's smaller, less attractive, tougher brother. Currently, its screen size tops out at around 94cm, although larger prototypes have been shown. LCD also hasn't come as close as plasma has to reproducing true blacks, and so isn't as ideal a choice for home theatre.

LCDs are extremely bright, however, making them ideal for well-lit rooms. They're also immune to burn-in and have long life spans -- up to 60,000 hours. These factors mean that in a few years, LCD could really challenge plasma in the larger-screen-size arena as manufacturing potential increases and new plants are built. For now, however, large, flat-panel LCDs are even more expensive per square centimetre of screen than plasmas.

Thinking of going big? Sure, you could buy a 160 cm plasma, but most people who want to maintain a good credit rating will opt for a rear-projection television (RPTV) instead. These sets start at about 100 cm diagonal, and the majority of them support the wide-screen, 16:9 aspect ratio and can accept high-definition signals. Here's an introduction to the choices.

Manufacturers still sell tons of CRT-based digital TVs, but over the next couple of years, other technologies will fall in price, and we'll witness their extinction. Tube-based RPTVs are not as bright as the other technologies described below and require regular convergence adjustments to maintain alignment of the red, the green, and the blue CRTs. Many such sets also suffer from relatively narrow viewing angles, where the picture becomes dimmer and/or discoloured when you watch from any angle other than straight ahead.

Relatively low prices will keep CRT-based big-screens in the game for the moment, and some advances in the field have been made. Manufacturers are finally developing smaller, slimmer versions, although they're still bulkier than the alternatives. CRTs also offer the highest picture quality, including those elusive blacks, of any rear-projection technology -- provided that you watch in a relatively dim room on a well-adjusted set.

We've been talking about black levels a lot, so let's finish the discussion right here: Aside from CRT models, digital-light-processing (DLP) sets currently provide the best blacks of any projection technology. DLP-based RPTV also have a 1,280x720-pixel-resolution chip that shows every pixel of 720p HDTV, resulting in a very sharp picture that doesn't need to be adjusted periodically. That's not as much resolution as you'll get from some LCD-based rear-projectors, however.

One big problem with early DLP sets is known as the rainbow effect. Some people can see streaks of colour on these TVs, especially when moving their eyes across the screen. The occurrence of these rainbows has been significantly reduced with the advent of newer, faster colour wheels, which are used to separate the internal lamp's light into colour before it hits the chip. In terms of price vs. performance, DLP leads the pack of CRT replacements for the moment.

LCD rear-projectors are generally ultraslim, big-screen models with even higher resolution (1,366x768) than DLP sets, and good colour saturation. They are also usually very bright, so watching in a well-lit room isn't a problem.

That said, they can also suffer from unimpressive black-level reproduction. LCD works by transmitting light through the chip, much like a photographic slide, so some light always gets through and makes for less than ideal blacks. We've seen significant improvement in the black levels of LCD front-projectors, so it will be interesting to see if newer RPTV versions follow suit.

At the top of the screen-size ladder, you'll find displays that don't really qualify as TVs: front projectors. These light cannons can easily fill 250 cm screens, but they're not for everybody since they require a light-controlled environment. Plus, for optimal picture quality, you'll want to buy a dedicated screen, although you can use a white wall in a pinch. Screen makers such as Stewart have special, low-gain screens designed to improve black-level performance for LCD and DLP projectors.

CRTs are also used in front-projectors; think of those three-tube monstrosities that hang from the ceiling in the coach compartments of older airplanes. We won't discuss them here, however, namely because CRT projectors are quite expensive and are generally reserved for high-end, custom installations, where they put the local cineplex to shame.

DLP and LCD projectors, on the other hand, often cost much less than their rear-projection cousins. Both technologies project the kind of huge picture -- from units as small as a shoebox -- that you enjoy at the theatre.

Much like rear-projection models, front-firing DLP projectors beat out LCDs when it comes to making inky blacks. On the flip side, they're not quite as good at filling large screens with light, so you may want to choose LCD if you're using the projector mainly for presentations. A few viewers may also see the rainbow effects that we described in the DLP rear-projection section.

The least expensive DLP projectors start around $2000 and use SVGA-resolution chips (800x600). That resolution is not high enough to display full HD TV, but it's nearly sufficient to capture every line of wide-screen DVD, which calls for 852x480 resolution. In practice, most of these models look well detailed with both HD TV and DVD. Step-up sets offer 1,024x768 or even more expensive 1,280x720 resolutions, for a corresponding increase in detail. However, only the 1,280x720 versions can display every detail of 720p HD TV, and their 16:9 aspect ratios are tailor-made for home theatre.

LCD and DLP are very close in terms of performance, and even LCD's ability to produce good blacks -- often expressed as a contrast ratio in projector specs -- has improved quite a bit. DLP still enjoys a slight edge, however, balanced by LCD's generally higher light output. LCD's colour fidelity, its ability to produce rich, saturated colours, can also beat that of DLP in some cases. LCD projectors offer a similar selection of resolutions as DLP models, although higher-end projectors use 1,366x768 LCD chips.

	Direct-view (tube) TVs What's new with the tube.

	Flat-panel TVs Slim is in, but plasma isn't LCD. Learn the difference.

	Rear-projection TVs Big-screen boxes come in many flavours. Taste them all.

	Projectors (Front-projection television) Prices for projectors are way down, and the images are getting better.

By David Katzmaier, CNET.com on 28 July 2004

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