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How to (and how not to) buy a flat-screen TV

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Part 2: Choosing from the new ABC and 1-2-3 of TV What type of flat-screen TV should you buy? LCD, LED, or Plasma? HD or HD Ready? 50Hz, 100Hz, 200Hz? In the second of a series of articles on the do and do not of flat-screen TV shopping, our new Audio-video specialist writer, JOEL KOPPING, warns that the numbers are not all that they seem.

If you’ve done your homework ‚ i.e. working out your home set-up and requirements (click here to see yesterday’s article), you can start looking at what types of flat-screen TVs you’ll see in store.

Most new flat-screen TVs use LCD ‚ Liquid Crystal Dyesisplay – or Plasma technology.

There are currently two types of LCD TV: traditional LCD TVs and so-called LED TVs. Both technologies work by using a light behind the LCD screen. The electronics in the TV tell the liquid crystals in the screen how much light to let through for us to see.

In traditional LCD TVs the light used is called CCFL (essentially similar to those fluorescent tubes you have in your kitchen) and LED TVs use LED (light emitting diodes) for their source of light.

LED LCD TVs tend to be thinner, use less energy, and are supposed to offer better black levels than more traditional LCD TVs. LED models also tend to be higher up on the totem pole and usually feature better image processing than traditional LCD TVs.

However, your choice must take account of the situation in the room where it will be used. If you don’t have a room that can be darkened, you could make a choice that might make your TV viewing a nightmare during daylight hours.

A general rule of thumb is that LCD TVs work better and deliver better image quality in bright rooms than Plasma TVs.

Plasma TVs don’t have a back-light: they have phosphors and gas that will glow brighter or dimmer depending on how much energy is fed to them. Precisely because they have no back-light, Plasma TVs tend to have better black levels than most LCD type screens. Plasma TVs also tend to deliver more natural colours than LCD TVs. However, these nuances will be lost in a well-lit room.

Making the choice

The question now is, why should you choose one technology over another?

If you are a video fan and have to have the absolute best in video quality, natural and lifelike colours, then a good plasma is possibly the way to go.

Plasma would probably be a good idea for gamers too, as Plasma images tend to be smoother and less likely to suffer from image blurring than their LCD competition. You do, however, have to remember that room lighting has to be controllable and controlled.

LCD TVs have come down so much in price, and for most viewing deliver such great images, that as a value proposition conventional LCD TV is really hard to beat.

LED back lit models usually cost a fair bit more than their conventional LCD stable mates but they offset their pricing by typically delivering better black levels, and smoother images. Some models are supremely sexy too, and look far more stylish than virtually any other TV technology. But again, remember that lighting is key to appreciating their quality.

Specifications

It’s now time to move on to specifications: those little nuggets of information that are there to confuse us.

Contrast Ratio:

In its purest form, Contrast Ratio is simply the brightest image a TV can display divided by the darkest image. Good contrast is vitally important if your TV is going to be able to display detail in bright and dark areas of an on-screen image.

Unfortunately, manufacturers tend to be rather creative when measuring contrast ratio. More often than not we are given a Dynamic Contrast measurement and this measurement, as mentioned in Part 1 (click here to read it), tells us little about how much detail a TV will actually be able to display, or how accurately it will display colours or motion.

While I won’t go into detail here on how manufacturers get to their claimed Dynamic Contrast ratio figures, I will say that the best I’ve measured in home type viewing conditions is around 1000 to 1. This is a far cry from the millions to one Dynamic Contrast often quoted.

While contrast ratio can be important, you need to be aware that it is a rating that can be manipulated. Trust your eyes: if one TV looks to have better shadow detail and darker black levels than another, it probably has, irrespective of what the other manufacturer claims.

Response time:

This is a measurement of how quickly the liquid crystals twist to allow light to the screen or to block light. While manufacturers also aren’t quite as honest as they could be about how they derive these figures, typically the smaller the number the better. Gamers in particular should look at response time when looking for a new TV.

Some manufactures are claiming response times as low as 2ms (milliseconds). At this pace you should see clear and clean image motion without image blurring. 4 ms is good too, but you probably wouldn’t to buy a TV that has a response rate much higher, especially if you are going to watch sport.

Refresh rate:

This sometimes gets confused with Response time, but they are different.

Refresh rate refers to how many time per second a TV draws an image on screen. Most entry-level TVs use a 50Hz refresh rate, and this is just fine for watching general TV. If, however, you watch a lot of sport or are a gamer, then you will want a TV with a faster refresh rate. Models that use 100 or even 200 Hz refresh rates tend to make moving images look a whole lot smoother and easier on your eyes.

Theoretically, faster refresh rates are better than lower ones, but you’ll see a bigger diference when moving from 50Hz to 100Hz than you will when moving from 100Hz to 200Hz. Unless you’re really into watching a lot of sport or play a lot of games, 100Hz TVs should deliver more than adequate video quality.

Incidentally, American/NTSC models have a refresh rate in multiples of 60 (120, 240). This is based on the powerline frequency. In South Africa, the United Kingdom and many PAL regions where the powerline frequency is 50 Hz, we get multiples of 50. A US spec TV would therefore be a 240 Hz model but the SA one would be 200Hz. Most product managers don’t know this, so don’t expect anyone on a shop floor to explain it to you.

Full HD or HD Ready:

There is a good reason why this specification is mentioned last. It is that aspects such as colour quality and saturation, image motion and good contrast are actually more important.

That said, HD Ready refers to resolutions of 720P (progressive) and above, while Full HD sets display a resolution of 1080P (1920 by 1080 pixels progressive).

While there are several iterations of HD Ready, the two most common are 720P (or 1280 by 720 pixels progressive) or 1080I (1920 by 1080 pixels Interlaced)

It is worth noting that true 1080P (and not up-scaled video, which deserves an article all of its own) is essentially only available from Blu-ray. In South Africa, DSTV HD broadcasts (DSTV are the only South Africans broadcasting in HD, and will be for the foreseeable future) are all in HD ready form, and all DVDs and other off air TV is in Standard Definition (576 by 720 pixels) or SD.

It is also worth mentioning that all TVs, when receiving SD signals, will convert these to either Full HD or HD Ready (depending on the resolution of the TV) and that better TVs do the conversion from SD to HD better than lesser TVs.

While logic indicates that Full HD is better than HD Ready, the reality is somewhat different. A good HD Ready TV will deliver better overall image quality than a bad Full HD TV. This means that you shouldn’t discount looking at HD Ready models that are in your budget just because they aren’t full HD. Quality beats quantity every time.

In the next edition in this series, we will move on to what to look for in store. Look out for it on Monday.

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