LED, LCD and plasma TV: Buying a new TV When you're in the store

Some problems are more obvious in
fast-moving scenes

TV sales staff often use screen resolution and contrast ratio figures to impress customers. However, all LCD, LED and plasma TVs use digital processing software to put a picture on the screen. Unless it’s spot on, this process, known as up-scaling and de-interlacing, can lead to unpleasant side effects.

Instead of being wowed by the ‘higher the better’ numbers orthodoxy, use your own DVDs, with some of the scenes suggested below, and try these simple approaches to get a better idea of the real picture quality.

To find the best HDTV for your needs, check our independent TV reviews.

TV problems to watch out for

Smearing 

A ghost-like effect, often visible on moving images. You’re unlikely to spot this on TV displays showing simple, colourful images – cartoons, say – so watch a football match instead.

Picture judder 

Like smearing, this is more easily spotted on real-life fast-moving action and panning shots. Images fail to move smoothly across the TV screen, instead making slight stuttering and juddering movements. 

In an attempt to manipulate the picture and create the illusion of smoother motion, many LCD and plasma TVs feature 100Hz processing software. This basically doubles the number of frames on screen per second from 25 to 50.

200Hz processing software quadruples the original frame rate, and places 100 frames on the screen every second. Typically motion processing software will make images appear smoother – but sometimes at the expense of a natural-looking picture.

Many brands claim even higher-sounding processing (600Hz for instance), but this is measured in a different way and our expert viewing panel has not reported any significant improvements in motion performance.

Look for jagged edges on images of buildings or text

Edges 

Watch out for over-enhanced edges on images, such as buildings or text. High-resolution HD TVs sometimes over-sharpen pictures, leading to jagged lines.

Over-enhanced pictures can lead to especially poor results when watching lower-quality digital TV broadcasts.

Sometimes a softer picture helps to disguise the grainy picture noise associated with the digital TV signal.

Skin tones on a face may appear in bands rather than blending

Colour banding 

When watching a sunset, for example, instead of different shades of colour subtly blending into one another, colours appear in distinct bands.

TV screen reflections 

Keep an eye out for screen reflectivity. LCDs tend to reflect the least – plasmas are not quite as good. CRT screens are made of glass and tend to reflect more light than either. LCD TV pictures often look a bit washed out, though this is less of an issue than it once was. 

Check out a movie with very dark sequences, like The Matrix, and see how much detail you can pick out.

LCD TV colour-fade 

The colour on some flat-screen TVs starts to fade when not viewed head on. LCD TVs are particularly susceptible when you view from acute angles but it's less of a problem for plasma TV screens.

Watching 3D TV 

It's early days, but the Which? lab has found the 3D effect on the TVs we've seen impressive. However, though you'll get a great sense of depth, we've encountered some problems with these TVs. 

We found the 3D effect diminished the further you sat from the screen. To get the best effect you have to sit much closer to the TV – around 1.5 metres away compared with the typical 2.5 metres for watching a high-definition picture.

Also look out for intermittent 'ghosting' – a faint double image – on background images, dimmer-than-normal pictures (thanks to the glasses) and jittery motion.

For more information, check out our 3D TV essential guide or results of our first 3D TV test

HD TV source 

Check the source of the picture you're watching in the TV showroom – TVs in stores often screen HD pictures. This will give you an idea of how good HD can be, but is certainly not representative of the picture quality you'll get via DVD or especially a standard broadcast signal.

Something plugged into the HDMI socket round the back of the TV is a dead giveaway that you're being shown high-definition images.

Viewing distance and HD TV screen size

Huge screens do justice to the extra detail of high-definition pictures, but may not be the wisest choice if you just want to tune in to regular standard-definition Freeview broadcasts. If you're replacing a 32-inch TV with a 42-inch model, for instance, the new TV should be viewed at an equivalent (further) distance.

Basically, the bigger the screen, the more you will see picture imperfections if you sit too close. For standard-definition TV the optimum viewing distance is approximately 6x the picture height. 

To find the best HDTV for your needs, check our independent TV reviews.