Choosing the perfect television for your lounge room requires more than just a ruler. Sure big is beautiful, but the proof is in the viewing.

Screen Size

Before you rush out to buy the biggest television you can afford, stop to think about the space it will live in. The distance between your couch and your screen should be between two and five times the width of the screen. Any further away and you'll start to lose the fine detail, but any closer and you'll be distracted by the individual pixels.

Also think about your home entertainment cabinet - is it big enough to handle your new pride and joy or will it need upgrading as well? Most new televisions are rectangular like a cinema screen, a shape known as "widescreen" or "16 by 9". Televisions are measured on the diagonal, so if you're upgrading from a squarish "4 by 3" set to widescreen you need to go up a few inches if you want the screen to be the same height.

Also give some thought to the layout of your lounge room if you're considering a technology prone to narrow viewing angles, such as LCD or rear projection. Narrow viewing angles can mean the picture appears too dark for viewers not sitting directly in front of the screen.

Display Technology

Flat is the new black when it comes to big screens. Television makers are phasing out bulky old CRT (Cathode Ray Tube) televisions in favour of slimline LCD (Liquid Crystal Display) and plasma sets. They're collectively known as "flat panel" televisions but are sometimes incorrectly referred to as "flat screen" - whereas flat screen actually refers to CRT televisions that don't have a curved screen.

While the battle between plasma and LCD gets most of the headlines, both still struggle to match the image from a good CRT. Even so, the size and weight of CRTs make it impractical to build them larger than around 37 inches.

If size matters, rear projection televisions go up to around 70 inches but they've traditionally been bulky units with very narrow viewing angles. Rear projection has made significant advances with the move to new projection technologies such as LCoS (Liquid Crystal on Silicon).

As always there are new technologies on the way, with OLED (Organic Light-Emitting Diode) set to replace LCD. OLED doesn't require a backlight so it can offer greater contrast, less motion blur and lower power consumption than LCD. The technology is already used for small displays such as on mobile phones and digital cameras. Sony is launching the first OLED television later this year in Japan, but it only measures 11 inches.

Other new technologies on the horizon include SED (Surface-conduction Electron-emitter Display) and FED (Field Emission Display).

Resolution

Resolution refers to the number of dots, or pixels, used to make up an image. The two common resolutions of high definition televisions are 1366x768 pixels (known as HD) and 1920x1080 pixels (known as "True" or "Full" HD). Televisions are available at a range of other resolutions including 1024x1024, 1024x768 and 852x480 - sometimes using rectangular pixels to create a widescreen display even though the resolution isn't 16 by 9. If such a televisions can display a downscaled HD signal, it's know as an EDTV (Enhanced Definition TV).

When it comes to high definition, a 1366x768 plasma is roughly the same price as a 1920x1080 LCD of the same size. Considering 1920x1080 is the resolution of Blu-ray, HD DVD and HD television, you'd think that 1920x1080 LCD would be better value for money, but there's more to a good television than just pixels. The proof is in the viewing, for example Pioneer's 1366x768 Kuro plasmas can look just as sharp as a high-end Sony Bravia 1920x1080 LCD.

Tuner

All True HD televisions should come with a built-in HD tuner, which lets you watch SD and HD digital television. Features such as Picture in Picture require two tuners. Some televisions come with one analogue tuner and one digital.

Take care when buying, as some HD televisions can still come with SD tuners - which means you can't watch the HD channels. The introduction of HD multi-channelling in Australia this year means you'll miss out on some shows if you can't watch the HD channels.

Brightness and Contrast

Television brightness is measured in candelas per square metre (cd/m2) and varies from 250 cd/m2 to up past 1000 cd/m2. LCDs are generally brighter than plasmas but anything over 400 cd/m2 should suffice in most lounge rooms. Brightness is important if you'll be watching a lot of television in a brightly lit room, otherwise you should pay more attention to contrast. Contrast refers to the ratio between black and white, for example 1000:1 means that whitest white is 1000 times brighter than the blackest black. Low contrast means your blacks look grey and you lose fine detail in the shadows. Plasmas generally offer greater contrast than LCD. Watch out for a form of voodoo mathematics used by LCD manufacturers known as "dynamic contrast". In dark scenes it drops the brightness of the backlight to create blacker blacks, but obviously at the expense of the bright spots in the picture. The difference between the blackest black in a movie's dark scenes and whitest white in the bright scenes is dynamic contrast, but you never see these on the screen at the same time. The difference between the blackest black and whitest white in any one frame is the static contrast. The use of rubbery contrast ratios means the number is only a rough guide to actual picture quality.

Response Time

Response time determines how quickly the pixels in an LCD screen can change colour and is measured in milliseconds. A high response time means fast moving objects, such as scrolling text, are more likely to blur as they race across the screen. Response times were initially measured as the time it took to change from black to white and back again, but today are usually measured as grey-to-grey - the time it takes to change from one shade of grey to another. There are several techniques to improve the response time of an LCD panel, such as "overdrive" which applies a higher voltage to the tiny liquid crystals.

Such tricks are often at the expense of image quality. Most new LCD televisions have a response time under 12ms, but there are so many different ways to measure response times, and so many so tricks to tweak them, that the figure has become almost meaningless.

Video Processing

Video processing is the black magic performed behind the scenes that separates the good televisions from the great ones. This 'x' factor is the reason why buying a new television isn't just a numbers game judged by pixel counts, contrast ratios and response times. The proof is in the viewing. Generally any television will look fantastic if you feed a perfect signal into it, such as a 1920x1080p Blu-ray movie. While giant televisions help high definition look its best, they also magnify any imperfections in the picture, so standard definition material can look terrible. Good onboard video processing ensures DVD, VCR and normal television still look their best. Live broadcasts of fast moving sport, such as AFL, are useful to judge how a television handles a less than perfect picture. Also take along your favourite movie on DVD, something you're very familiar with, and see how it looks on different televisions (using the same DVD player if possible). Look for motion blur, speckles of noise and pixelation - particularly in the shadows. Also watch out for straight lines that become jagged while the camera moves.

Connectors

The most important connector to look for is HDMI (High-Definition Multimedia Interface), the new cable format that combines digital video and audio in the one cable. Most high definition sources, such as Blu-ray/HD DVD players and HD Personal Video Recorders, use HDMI - so you need at least one HDMI input, preferably more.

 The HDMI inputs needs to be HDCP-compatible (High-bandwidth Digital Content Protection) for watching commercial Blu-ray/HD DVD movies. DVI cables can also carry high definition video, but require a separate cable for audio. If you'll be connecting a DVI device to a HDMI input via an adapter, ensure the television's HDMI port is accompanied by its own Left and Right audio inputs. Apart from HDMI, a new television should feature the usual suspects; composite, component, s-video and maybe SCART. Most flat panels also feature a VGA monitor input for connecting to a computer.

Look for inputs on the sides or front of the television, as well as the rear, if you'll be regularly plugging and unplugging devices such as video cameras and games consoles. If the television has a digital tuner, it should also have digital audio outputs (coax and/or optical) for connecting to a surround sound amplifier.

USB and Digital Photo Card Reader

USB ports and flash memory card readers are recent additions to new televisions, allowing you to run digital photo slide shows on your television rather than your computer. Some televisions will also let you play music and video files from a USB stick or memory card.

Compare over 150 + Plasma or LCD TVs...  

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For example, find all 42 inch high definition screen tvs; or find all LCD tvs with RRP between $2,000 to $3,000; or find all Pioneer Plasma tvs.

You can create a shortlist of the TV models you are interested in, then look for local retailers and deals near you. Confused about some of the terms? Find out more in our jargon busting digital TV glossary.

See other articles on digital TVs here, including a run down on Plasma Versus LCD tvs, HDTV in Australia and how we calculate our energy ratings for TVs.