The HDWars Guide to TV tech

As anyone who’s recently braved the packed shopfloors of their local electronics store will know, deciding what TV to buy these days is a seriously tricky business.

The amount of choice open to you is nothing short of bewildering, leaving you to try and pick your way gingerly through a maze of weird and wonderful sounding features; gaping price differences; online TV platforms; differing levels of multimedia playback via USB, SD card or even networked PCs; different types of tuner; and even a quartet of fundamentally different TV picture technologies.

It’s these picture technologies that this feature is going to get stuck into. For fully understanding the strengths and weaknesses of each of the four main current flat TV systems is essential if you want to make sure you buy the best one for your needs.

If you’re thinking here that you only know of two types of flat TV technology, plasma and LCD, don’t worry: you’re not going mad, and you’re not totally out of touch. It’s just that in our opinion, the three lighting variations possible with LCD – CCFL, edge LED and direct/rear LED – produce such performance variations that they really need to be thought of separately when you’re figuring out what to buy.

Plasma

Plasma technology kicked off the whole flat TV revolution, with plasma technology having been originally developed to deliver video playback on massive screens at the 1998 Nagano Winter Olympics.

Plasma screens are made up of rows of plasma cells, with each cell representing one pixel of picture resolution. Within each cell you get red, green and blue phosphors, a device for supplying current, and a gas that glows when fed that current. Each separate pixel is thus self-illuminating, rather than passively lit as is the case with LCD-based screens.

Plasma was once supported by almost every AV brand, but manufacturing difficulties and expenses have seen many brands defect to LCD, abandoning plasma completely.

Plasma’s main supporter is Panasonic, but Samsung and LG both make plasma TVs too, with other more niche brands including NEC and Runco.

The key pros and cons of plasma technology look like this:

Plasma pros

1 Wide Viewing angles

Because of their self-emissive nature, plasma panels are much more tolerant of wide viewing angles than LCD TVs. In fact, you can often be sat almost at right angles to a plasma TV before it loses significant contrast or colour.

2. Fast response time

Because plasma cells don’t depend on anything physically moving (liquid crystals have to open and close), they can react much more quickly to changes in image content. Panasonic quotes a response time of 0.01ms for its current mainstream plasma TVs, whereas typical LCD response times clock in at between 4ms and 8ms.

All this talk of milliseconds might not sound much on paper, but it can be the difference between moving objects retaining or losing clarity as they cross the screen.

3. Contrast/black level response.

The fact that each individual cell in a plasma screen lights itself has a very positive effect on plasma’s ability to produce dark colours, especially black. For when a plasma cell finds itself in a dark part of a picture, it can be told on an individual basis not to generate much light.

With LCD, on the other hand, the pixel array is driven by external light sources, making it difficult to control the light accurately on a pixel by pixel basis.

4. Consistent cross-screen light levels

Because each pixel in a plasma display illuminates itself, you don’t have to worry about some areas of the picture looking distractingly brighter than others during dark scenes, as can happen with all LCD technologies.

Plasma cons

1 Energy efficiency.

The fact that each separate cell has to be charged individually has created some tricky hurdles for plasma brands to clear in keeping up with EU energy targets. So far they’ve managed it, but although some plasma makers deny this, we’ve also had sources within the plasma world suggest that plasma performance standards might be affected if the energy consumption regulations continue to be tightened.

2. Colour balance.

Although this is much less of an issue than it used to be, some plasma screens still find it difficult to achieve natural, rich red and green colours. Various attempts have been made to counter this, from using elongated pixels with unequal RGB phosphor sizes to Panasonic’s recently introduced Red push technology. But rogue colour tones certainly still appear regularly on relatively cheap screens, especially when watching standard definition.

3 Image retention

If you keep a particular, bright, colour-rich image element – like a channel logo or video game ‘meter – in the same place on a plasma screen for too long, the phosphors ‘tire’ in that area, leaving a long-lasting, potentially permanent shadow of the bright item behind that’s clearly visible over other pictures..

Again, this is far less troublesome an issue than it used to be, with Panasonic in particular really getting to grips with it. But some recent plasma sets we saw from LG the 50PK790 and 50PK990) reminded us that the problem hasn’t completely gone.

Since the image retention issue is at its worst in the early life cycle of a plasma TV, we still urge anyone who buys one to be particularly careful how they use it for the first 100 hours or so.

4. ‘Fizzing’

The difficulty with regulating the current going into plasma cells can leave images looking slightly fizzy if you sit too close to them. Also, some plasma TVs can produce gentle dithering noise over fast-moving objects – especially skin tones. Though once again, this issue is far less common than it used to be.

5. Lack of brightness

Plasma TVs are generally characterised by a more muted look than LCD TVs. This can actually be a good thing in a home environment, but can certainly hurt the technology in shop ‘shootouts’.

Favourite plasma TVs:

Panasonic TX-P50VT20

This 50in masterclass from Panasonic shows off everything that’s good about plasma technology to a degree not seen since the heady days of Pioneer’s final KURO generation. And it delivers class-leading 3D performance into the bargain.

Samsung PS50C6900

This Samsung model is no match for the Panasonic P50VT20 in all-round performance terms. However, it’s still very good, and has another ace up its sleeve: namely that it’s unbelievably cheap. For despite being 50in across and carrying active 3D technology, at the time of writing it could be bought for just £950. Mental.

The CCFL LCD option

Despite originally being developed for relatively static computer display use, LCD TVs lit by CCFL bulbs have achieved exceptional commercial success since Sharp introduced the first ones.

Indeed, most key brands – Sony, Philips, Sharp and Toshiba to name but four – have now ditched plasma entirely in favour of LCD TV, and even plasma-loving Panasonic now does LCD options up to 42in.

The majority of LCD TVs continue to be built around the original CCFL lighting concept rather than the recently introduced LED alternatives we’ll get to presently.

LCD screens comprise panels of tiny light valves and regulators. A coloured filter sits in front of each valve, and in the case of the category of LCD we’re looking at here, a single, always-on bright CCFL backlight sits behind each valve (or cell). Each of these cells has its own opening and closing control system with which it decides the amount and polarity of the light that goes through it, and thus the part each cell plays in producing the final picture.

CCFL LCD pros

1 Price

Using simple CCFL bulbs behind LCD panels is by far the simplest, most cost-effective way to produce a flat TV, particularly at relatively small screen sizes.

2 Light consistency versus LED

While both edge and direct LED-lit LCD TVs all tend to have problems achieving light consistency right across the screen, it’s generally less troublesome with CCFL LCD TVs (though there are well-documented exceptions).

3 Brightness

CCFL-lit TVs generally have no trouble at all pushing out pictures with plenty of brightness and colour aggression.

4 No screen burn/image retention or fizzing

We’ve yet to see a CCFL LCD TV suffer with either of these plasma foibles. Where a CCFL LCD image looks grainy or bitty, it’s down to the picture processing not the core LCD Technology.

CCFL LCD Cons

1 Black level response

As film buffs, we love TVs that can produce a convincing black colour to do justice to all our favourite scary scenes. But sadly this is something CCFL LCD’s struggle to achieve.

The reasons for this are easy to understand. For CCFL LCD TVs illuminate their entire array of LC pixels from a single, always on light source. So clearly the ability to regulate the brightness level of individual pixels is limited, resulting in pictures that should look black tending to look grey and cloudy instead.

2 Brightness ‘jumps’

To try and get round its inherent black level problems, nearly all LCDs employ dynamic contrast systems, where the output of the CCFL light is reduced when the TV’s processors detect that a source picture contains dark content. But while these systems certainly do improve perceived contrast, they can also produce noticeable ‘skips ‘ or jumps in the image’s overall brightness level.

3 Limited single-frame contrast

When showing pictures containing a mixture of bright and dark content, the CCFL LCDs continually have to find a balance/compromise between reducing the brightness of the light parts of the picture in a bid to produce the dark parts convincingly, and reducing the depth of the dark areas so as not to completely remove all the punch from the bright bits.

4 Limited viewing angle

CCFL LCD’s reliance on a single light source behind the LCD array means that the light emitted from the screen emerges with a pretty small angle of dispersion. So images tend to lose contrast and colour quite drastically when watched from angles of 40 degrees or more – a potential real concern for people with large families or tricky room layouts.

Panasonic and Hitachi’s In-Plane Switching (IPS) LCD screens improve this problem quite a bit, but still not to the same level possible with plasma.

5 Relatively poor response times

The opening and closing element of LCDs means they struggle to respond quickly enough to changes in image content, leading to moving objects potentially looking low on resolution or smeary – or both!

Response times have been massively reduced over the years through a combination of mechanical and processing power improvements, but there are still few if any LCD TVs that are completely immune to motion problems. This is especially true with basic CCFL-lit models, with their largely static backlighting.

Favourite CCFL LCD TVs

Sony KDL-40EX503

The first TV we saw from Sony with a built-in Freeview HD tuner, the 40EX503 remains a terrifically no-nonsense 40in TV that produces excellent CCFL LCD picture quality from both its Freeview HD tuner and Blu-rays. It also introduced us to Sony’s excellent new Bravia Internet Video online platform.

Samsung LE40C650

Samsung’s Ultra Clear LCD TV panels have proven able for a couple of years to deliver some of the very best LCD pictures money can buy. And the LE40C650 is no different. In fact, the black level depths, colour saturations and sharpness levels it’s capable of producing are a revelation for its price point. Plus it looks lovely, and even gives you a Freeview HD tuner and Samsung’s Internet@TV online services for your money.

The direct LED-lit LCD option

First introduced (but quickly forgotten, oddly) by Samsung, LCD TVs with direct LED lighting illuminate using LED light clusters ranged behind the screen rather than a single CCFL bulb.

The initial direct LED-lit LCD TVs were the first to convince us that LCD really could take on plasma as a premium quality, film-friendly technology.

Fortunately, after a couple of years of other pretty cost ineffective direct LED options, direct LED screens are now becoming both more common and more affordable.

The basic idea behind using direct LED lighting is blindingly simple. First, LED lights are both more economical and more flexible to run than CCFL lights, with their ability to run stably at lower illumination levels than CCFLs being particularly handy. Second, having an array of lights rather than the single CCFL light source opens up the possibility of controlling each of the separate LED ‘clusters’ independently – AKA local dimming.

Direct LED pros

1 Much improved contrast

As noted a moment ago, LED lights can be dimmed to lower levels than CCFLs. This means practically all direct LED TVs produce markedly superior black level performances to CCFL LCD TVs. Indeed, the best direct LED TVs can even challenge many plasma screens for sheer black colour purity.

Direct LEDs that make use of local dimming can be particularly effective when it comes to contrast, thanks to the potential for one LED cluster to be firing at full power right alongside another cluster that’s producing practically no light at all.

2. Rich, dynamic colours

The properties of LED lighting generally seem to help produce a wider colour spectrum than other flat TV technologies. This is especially true with premium direct LED TVs like the Sharp XS1E and Sony X4500 models, which use (now pretty much defunct) RGB dimming technology rather than the more common white dimming.

3 No screen burn or fizzing

As with CCFL LCD TVs, direct LED LCD TVs don’t suffer with image retention or fizzing noise like some plasmas do.

4. High brightness levels

Having an array of LED lights driving the picture can really boost brightness levels, to the point where some direct LED images look positively luminous.

5. Energy efficient

LED lights are easier to drive than CCFLs, with the result that direct LED TVs typically use markedly less power than non-LED flat TV formats.

Direct LED cons

1 Missing shadow detail

While direct LED TVs that use local dimming can produce the richest contrast, they can also cause details in dark areas of the picture to go AWOL. This is because the number of LED clusters is small versus the number of pixels in the picture. Even the best direct LED sets currently have around 250 LED light sources, versus 1920×1080 pixels. So it follows that if you are turning some of these LED clusters off or low to try and produce good black colours, then individual bits of detail in those dark areas could go missing. It’s common, for instance, for direct LED TVs to show less stars during outer space shots than our other types of flat TV.

2 Haloing

Again because of the relative paucity of LED light sources versus the number of pixels in the picture, it’s occasionally possible to see subtle haloes or clouds of light around the edges of bright objects when they appear against very dark backgrounds.

3. Viewing angle

As with other forms of LCD TV, direct LED ones lose colour and contrast if viewed from an angle of more than 40 degrees or so. The haloing phenomenon described in point two also becomes much more pronounced during off axis viewing.

4. Motion blur

While often handling motion better than CCFL LCD TVs, many direct LED LCD TVs still lack motion resolution versus the best plasmas.

4. Expensive

Direct LED TVs – or at least the ones with local dimming – tend to be expensive.

Favourite direct LED LCD TVs

Philips 46PFL9705

If you can afford the Philips 46PFL9705H’s rather steep £1400 price tag, you really are getting the current state of the art in TV terms. The direct LED lighting system produces easily the best pictures we’ve seen from an LCD TV, with stunning black levels, extreme colour saturations, a massive contrast performance, and detail levels that are second to none. It’s also got Philips’ lovely Ambilight technology, Philips’ NetTV online platform (including full Internet access) and also exceptional sound quality by flat TV standards.

LG 55LX9900

With the 3D-capable 55in 55LX9900 LG has somehow delivered direct LED picture quality from a TV so slender it’s hard to believe it doesn’t use edge LED technology.

It’s hugely laden with features, too, and its 2D picture quality is outstanding, easily the best LG has delivered to date. Its 3D images are OK too, but suffer the inevitable (with LCD) crosstalk ghosting.

The Edge LED option

Developed initially to help manufacturers make TVs thinner, edge LED technology has also proved capable of delivering exceptional brightness and colour performances compared with normal CCFL LCD TVs.

As the name suggests, edge LED LCDs use LED lights ranged around the edges of the screen to illuminate the liquid crystal array, with the light shining across the back of the array and being angled through it by reflectors.

Edge LED pros

1 Slim designs

Not having a rear mounted light allows TV designers to think thin. Samsung’s new 9000 Series edge LED TVs have a frankly unbelievable depth of just 8mm.

2. Energy efficient

As with direct LED TVs, edge LED models run very economically versus plasma and normal CCFL TVs. In fact, some argue that edge LED sets are the most economical of all, since they don’t need to push their light through brightness-reducing diffuser plates.

3. Enhanced shadow detailing

The light created behind an LC array with edge LED sets is arguably more consistent and brighter than it is with direct LED sets. And since there are many more reflectors bouncing the light through the LC array than there are LED clusters in direct LED TVs, the points of light origin with edge LED sets are actually more closely related to the 1920×1080 pixel count of most of today’s TVs. This means that edge LED sets tend not to miss shadow details like direct LED sets can.

4. Rich, dynamic colours

As noted with direct LED TVs, using LED lights seems to boost colour response, with most edge LED TVs producing colours of eye-catching vibrancy and dynamism.

5. High brightness levels

Edge LED sets consistently do very well at delivering extremely potent brightness levels.

6. No fizzing or image retention

As with all our LCD screens, edge LED sets don’t suffer with the image retention or fizzing issues that can still affect some plasma TVs.

Edge LED cons

1. Black level response

Since edge LED TVs don’t permit local dimming in the same way that direct LED TVs do, most have to resort to the kind of general, whole-picture and thus not particularly satisfying dynamic contrast compromises noted with CCFL LCD TVs.

2. Local dimming doesn’t work

Three brands have tried to introduce local dimming to their edge LED TVs, by allowing groups of lights in the screen’s edge to be controlled independently. But this creates noticeable ‘blocks’ of light inconsistency when bright objects appear against dark backgrounds.

3. Backlight inconsistency

Even edge LED TVs that don’t use local dimming tend to suffer with backlight consistency issues. With many edge LED TVs, during dark scenes you can see patches of clouding, particularly at the edges and in the corners.

Favourite edge LED LCD TVs

Samsung UE46C8000

This iconic TV completely epitomises the glamorous design edge-LED systems make possible. It’s a terrific 2D performer, too, with an enormous feature count and multimedia talents galore. Its 3D is good too, but does suffer with crosstalk noise.

Sony KDL-40HX813

Although this set is expensive for a model that makes you cough up extra for its optional 3D kit, there’s no denying its excellent picture quality combined with superb multimedia capabilities. There’s still crosstalk on its 3D pictures, but seemingly slightly less than with other 3D LCD TVs.