Top-TV UK buyers guide for high definition television

Buying a new TV is not what it used to be. Today's flat screen LCD and Plasma TVs have complex technical specifications that are hard to compare. You need to make sure that you get one with the right features and performance characteristics that will not become obsolete too quickly. The EICTA (European Information & Communications Technology Industry Association) has defined a minimum standard for High Definition (HD) televisions which requires the set to have a widescreen format with at least 720 lines, suitable input connectors and colour support to work correctly with today's HD receivers. Any TV marked as "HD Ready" in Europe must meet this standard. However, the standard is not particularly strong, and should be taken as just a starting point for your choice of TV.

To help you, our experts at Top-TV have devised this technical guide which covers the main points you need to think about when buying an HDTV. The guide is designed to be sufficiently simple for anyone new to the technical aspects of HDTV, yet deep enough to cover all the significant details you should be taking into account. To accompany this guide, Top-TV maintains a list of over 500 HDTV models available now in the UK along with their product details. You can bring up this list at the same time as you work through this guide and use it to narrow down your shortlist of TVs to choose from. Click on the "more info" links in the list to see further details and compare prices.

Click here to bring up the Top-TV list.

Size and Resolution

As a first step you need to fix the size and resolution for your HDTV screen. The screen size (usually measured in inches) is the diagonal size of the display area measured from top left to bottom right. When shops used to sell the old tube TV sets the manufacturers could get away with quoting the size of the glass which extended beyond the visible screen. With LCD and Plasma TVs they are no longer allowed to do that, so you can be sure that the quoted size is the actual size of the picture you will be viewing. This means that a 32 inch flat screen TV has a slightly bigger picture than the 32 inch telly you were used to. Furthermore, the new technology allows much larger screens to be fabricated and the sweet spot that the panel makers are targeting for highest production volumes is now around 46 inches. Of course you need to take into account the space you have for it in the living room and your budget.

The size of your screen also needs to be consistent with the screen's pixel resolution and the typical distance you view it from, so let's look at the different resolution standards next. The resolution is usually quoted in terms of the size of the matrix of pixels which make up the screen. For example a resolution of 1366x768 means that the picture is made up of an array of dots in 768 lines down the screen, each having 1366 points across. That makes about one million pixels in total. As you probably know by now, there are two main resolution standards in use for high definition TV. The base HD standard of 720p is 1280x720 but there is also a higher standard known as "Full HD" or 1080p which has a resolution of 1920x1080 pixels. You should compare these with the standard definition (SD) widescreen pictures using the old PAL system which were equivalent to a resolution of 1024x576. In fact, as can be seen in the diagram below, the 720p high definition standard is not massively bigger than the PAL standard. It was really defined with the US standard NTSC in mind which had a much poorer resolution. For European viewers there is much more incentive to opt for a screen which supports the higher Full HD standard. Many HD TV channels broadcast with a data bandwidth that would not justify Full HD resolution, but HD-DVD and Blu-ray disks provide a much higher quality picture that needs a Full HD screen for the best appreciation.

So a Full HD purchase is certainly justified for the ultimate home movie experience, but it is going to be more costly than 720p and would be a waste of money if your screen is not big enough relative to your normal viewing distance. The viewing table below should be used to help you choose the right screen size for your circumstances. For example, if you are aiming for a 40 inch HDTV and your typical viewing distance is 8 feet, then it falls into the 34"-42" range that indicates you should get a 720p resolution screen. There would be no point in buying a Full HD screen at that size and distance unless your eyesight is significantly better than average.

LCD or Plasma?

Now that you know the size and resolution you want to go for you are ready to choose between the two main competing technologies for flat screen TVs: LCD or Plasma. LCD panels use a backlight which shines through a liquid crystal pixle matrix. By applying currents the crystals can be made to block the light and control the intensity of the pixle for each of the three primary colours. Plasma screens use a very different principle which does not require a backlight. Each pixel of the image is generated from a plasma cell which emits its own light.

You can find many articles on the web comparing the relative merits of the two technologies but beware, many of them are written by the panel manufacturers and have a strong bias one way of the other. We would summarise the complex and changing circumstances with these bullet points:

• In general, the picture quality from a plasma display is higher. Plasma displays produce higher contrast ratios, shorter response times, a wider range of colours and brighter images than LCD panels.
• LCD displays are much easier to make in smaller sizes and at higher resolutions than plasma. As a general rule your choice of plasma displays will be limited for 720p below 40 inches, and 1080p below 50 inches.
• Plasma displays have some operational disadvantages. They use more power and need to be "run-in" carefully to prevent screen burn. They may also have a shorter lifespan. However production improvements mean that these issues are not as significant as they once were.
• Some LCD models have suffered from backlight problems which cause various image nasties known as "clouding", "banding" or "backlight bleed". , These effects are rarely noticeable during normal viewing except in the most extreme cases. Better manufacturing standards and quality control should hopefully have eliminated them altogether on the latest models.
• The picture quality of LCD displays has been greatly improved with the use of various electronic tricks. These include dynamic contrast control, 100Hz refresh rates and wide colour gamut backlights. You will find these features and more available on the top range models.

If your time for researching these features is limited the best advice we can offer is that with the major brands you get what you pay for. The higher priced newer models all have an exceptional standard while the lower priced older versions are still very acceptable.

Integrated Freeview and HD Connectors

The next thing to think about is what you want to connect to your TV and whether it needs an integrated Freeview tuner. Of course Freeview does not provide HD programs so having one should not be a major concern if you are primarily interested in HD viewing, but it may be a welcome extra that helps you narrow down the selection. Many people find that they are disappointed with the quality of their SD pictures on HDTVs. This is partly because the screen is bigger. If it does not fall in the range for PAL resolution in the table above then you will be viewing it too close and will see effects of the low resolution. Another factor is that the inbuilt Freeview tuners often do not have sufficiently good electronics to filter the noise from the pictures. If viewing SD content is important to you then we recommend that you use an external Freeview tuner and a good upscaler designed for the purpose. The same goes for standard DVD content.

All external devices will of course need to be connected. Any HD reciever or DVD player should be connected using an HDMI cable. The same goes for HD game consoles such as the Playstation 3. An XBox 360 can use component connections and other inputs can come via s-video or composite connections. Finally, your legacy equipment may use scart so the TV should have those too. It is important to work out how many of each connector type you are likely to need and ensure that the HDTV has them. For example, if you are connecting Sky HD, an upscaling DVD player and a playstation 3 that already adds up to three HDMI inputs. HDTV sets mostly come with 1, 2 or 3 HDMI inputs depending on how far up the range they are.

It is worth bearing in mind that there are different versions of HDMI and some models of TV are now boasting HDMI 1.3 support. This version is designed to allow for better sound input and digital video signals with a higher colour depth such as 10 bits. However, sporting an HDMI 1.3 socket and providing the capability to process the improved signals are two different things. Furthermore, there are not many sources of input that could take advantage of this standard. For the time being the HDMI 1.3 standard should not be considered as very important.

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Sound

If you are aiming for a top HD TV then no sound system built in to the TV will be adequate to complete your system. You will need to purchase a separate surround sound system with multiple speakers. This might come in the form of a good "home cinema" system which includes a DVD player as well as speakers. However, for a lower specification you can make do with the inbuilt system and some HDTVs have quite good performance "virtual surround sound" speakers. Don't be fooled though. These cannot in any way match real surround sound.

Other Performance Features

We have already covered most of the things you need to think about except the look and style of the TV. However, if you are a real perfectionist and want the best that is available there are a few other performance features you should consider. For your convenience we list the main specification features relating to picture quality that you should lo0k out for.

• Screen resolution is the size of the array of pixels on the screen. The most common figure is 1366x768 which is slightly above the 720p standard. 1920x1080 is needed for Full HD. Sometimes other sizes are used but they do not usually work so well.

• Static contrast ratio is the ratio in brightness of the lightest to darkest levels that can be shown on the screen at different points of one frame. A higher static contrast ratio usually means better levels of black.
• Dynamic contrast ratio is the ratio in brightness of the lightest to darkest levels that can be shown on the screen in different frames. For plasma displays this figure is the same as the static contrast ratio, but LCD displays can improve the dynamic contrast ratio by varying the backlight intensity from one frame to the next. Having a high dynamic contrast ratio is not as good as having a high static contrast ratio but it is still an important indicator of video quality because film frames often vary widely in overall brightness.
• Brightness measures the light intensity of the screen in candela per meter squared (cd/m²) also known as "nits" for brevity. a high brightness ps better but most screens are sufficiently bright in typical home lighting, so this number is not as important as contrast ratio.
• Response time is the time it takes to change the brightness and colour of the screen. Plasmas generally have a very fast response time while LCDs have longer response times around 8 milliseconds. This can mean that some blurring is seen on LCD displays when viewing certain types of motion such as panning. On some LCD displays electronic tricks are used to significantly reduce the problem.
• Viewing angles show the range of angles at which the screen can be viewed without loss of brightness. The viewing angles are usually more than adequate except on some smaller LCD displays
• Colour depth is the number of bits used per colour channel to control the level of brightness. plasma panels usually have very good colour depth but LCD displays often work at just 8 bits. This can cause visible colour banding on images of slowly varying colour. Once again the LCD makers have been able to get round this limitation by having 10 or more bits for colour depth in the video processing engine of the TV and then using a dithering technique to increase the variation of colour on the panel. Although this is not quite as good as having 10 bit panels, it does work very well and the colour processing depth is usually what is quoted on the spec sheet.
• Frame refresh rate is the rate at which the Tv image changes. The normal frame rate in Europe is 50Hz but some LCD Tvs now use a higher 100Hz frame rate to reduce motion blur. This is not necessary for plasma displays.
• Colour gamut is the percentage of visible colours that can be displayed. LCD panels often only cover about 50% of the range that the eye can discern whereas plasma screens cover 100%. Higher range LCD displays have wide colour gamut backlights that greatly increase the range of colours and they can often cover the full visible spectrum. This is a very important feature to look out for if you seek the best image quality from an LCD panel.

That covers most things that people will want to think about when buying an HDTV except operational numbers such as power rating and standby power consumption which speak for themselves. Now you are ready to select your TV using our list. Click on the "more info" links to get the full details for each TV, then click on the "compare prices" button to check the last important figure: how much it costs!