How Plasma TV works: technology explained, vs LCD, 4K and the future of plasma

As things stand now, you have a choice of three technologies when deciding on your next TV. You could buy an LCD TV – often, somewhat erroneously called LED TVs. If you have loads of money, OLED TVs are an option, but only LG and Samsung are really offering even vaguely affordable OLED TVs right now. The last option is plasma, a darling of TV reviewers, but what makes it special, and how does it cope with modern technologies, such as 3D and 4K along with the must-have smart and catch-up TV functionality?

Most of us have heard of the various different technologies that make up the TV market in the UK. Right now, as you might expect, LCD TVs are going great-guns, and make up the largest proportion of sales, while plasma TVs are slowly losing ground and OLED TVs are really just getting started. Ultimately, most of the TVs on sale now have the same smart functionality, such as access to Netflix, Amazon Instant Video and BBC iPlayer right from the TV’s menu system, the differences are about how the image is displayed.

A history of plasma displays

Before 3D, plasma and LCD, there was really just one display technology, and it remained largely unchanged from when TV broadcasts started until the mid-2000s when we started to see the first LCDs and plasma TVs. This technology was called CRT, or Cathode Ray Tube. Simply put, a glass screen was blown, like any glass is, and turned into a tube, which was vacuum sealed. A coating of phosphors on the front in red, green and blue would then glow when a scanning electron beam struck them from behind. Electronics, and your eyes’ persistence of vision would turn this into a solid, stable picture (see our History of TV feature for the full story).

The fundamentals of TV haven’t changed much since. LCD TVs and plasma screens do things differently to each other, but those red, green and blue points of light remain the same but how they are made to “glow” is different.

Plasma TVs are actually very similar to CRTs. Instead of having a beam that scans, a plasma produces light from its pixels when an electric charge is applied to a cell containing a noble gas, or “plasma”. These plasma chambers are sealed units, the gas will never escape, so any rumours you’ve heard about plasmas needing re-gassing is just an urban myth.

It’s also fascinating to note that plasma display technology was first considered in the late 1930s by Hungarian engineer Kálmán Tihanyi. By the 70s, there were actual monochrome displays in use based on technology invented at the University of Illinois for the PLATO computer system. While this technology is very different to modern colour displays, the University of Illinois would later work with Japanese broadcaster NHK to turn the system into one suitable for colour TV reception.

The first proper plasma TVs, as we know them today, were manufactured around 1995 by Fujitsu and Philips. They weren’t HD sets, and they cost more than £10,000. In 1997 Pioneer began selling TVs to the public, and thus began a new era.

What are the advantages of Plasma over LCD and LED TVs?

During the early years of flat panel TVs, much was made of which technology was better. These days the differences are much smaller. Plasma has improved its weak areas, and LCD has done the same. Picking a TV now is really more about features than picture quality, because these two technologies are so close.

For many, the big advantage of plasma was that it was able to produce better black levels. To understand why, we need to look at the technology and how it produces an image. In a plasma TV, the cell in which the gas is contained creates its own light. This means that when an image is made up of contrasting light and dark areas, the TV can produce nearly perfect black where it needs to. The control is accurate to the pixel.

On an LCD TV there are two types of backlight. The first is called CCFL (cold cathode fluorescent lamp), and has mostly disappeared now. But in the early days, it was this that caused LCDs to have such problem producing deep, rich blacks. This is because the light would shine constantly, and while dimmable if the scene as a whole was dark, if there was a mix of light and dark at the same time, you would see very washed out blacks.

LED backlights then appeared, and these came in a further two variants. Either edge LED or “full” LED backlights. Edge LED was similar to the CCFL system, it meant TVs got very thin very quickly, but it didn’t really produce better black levels. Full LED, as it became known, was a large number of very small LEDs mounted directly behind the LCD screen, grouped into zones. These zones could be individually “locally dimmed”, which allowed for scenes of mixed light and dark to be reproduced with better black levels.

As a rule, cheaper LCDs would have edge LED lighting, while more expensive models would have the “full” LED backlight. This was all developed as a way to compete with the plasma displays, which did the same thing simply by virtue of their emissive cells.

While plasma was a great deal better with blacks, in a fully darkened room many plasmas would have noticeable glowing, or if you were very close to the screen you would be able to see blue speckles. As the technology evolved, this artefact went away, but even at its worst, it still was never as bad as the crushed blacks from LCD TVs.

Are there disadvantages to plasma TVs over OLED, LED and LCD TVs?

As with any technology, nothing is perfect, and plasma’s had its share of problems. For many years plasma TVs were horrendous power hogs. The bigger 50- and 60in TVs would consume hundreds of Watts of power, and cost loads of money every year.

Plasmas also get hot, and because of that they need to be cooled by fans. Mostly, these fans were well-designed, but sometimes they would be loud and intrusive. The heat issue on some large TVs was borderline comical, but in winter it would help keep your house warm.

Much was also made of image retention. This was a problem on CRT TVs too, where if you left a high-contrast static image on screen for an extended period – say 30 minutes – you would still be able to see it after the image was changed. This would usually clear itself after a while though, although in early plasmas permanent screen burn was a real concern.

It’s worth remembering that a plasma TV is most susceptible to burn during its first 100 hours of use, so be a bit more careful when your TV is new, then you can relax a little after a few weeks.

Plasma 3D TVs

Like LCD and LED TVs, it’s perfectly possible to get great 3D on a plasma TV. There are a couple of things to remember though.

Plasma TVs can’t do passive 3D. This method of displaying 3D is nicer to use, although it has a disadvantage in that it’s half full HD resolution. For plasma sets, you must have active shutter 3D, which uses a set of powered glasses to produce a 3D image.

Active is very good at producing 3D, especially on modern TVs. The glasses are light now too, and usually rechargeable with hours and hours of battery life. You also get a 1080p 3D image, which gives crisp, detailed pictures. Because of the very quick response time of plasma screens, you also get no 3D ghosting – where the image for left and right eyes collide, giving you a double image – which is a real advantage.

The worst part of 3D on a plasma TV is that it reduces the brightness of the picture. Modern plasmas are quite bright, but you’ll still notice that your movie looks a lot darker than it does in 2D. That said, if you’re serious about your movies, you’re not going to be watching in a very bright room, and will probably have invested in blackout blinds so you can comfortably watch during the day.

PLASMA TVS AND 4K

Here’s where plasma’s future started to come undone. While there were only minor problems in creating 3D-capable plasma TVs, 4K is much harder. You need to find a way to fit a lot more pixels on the screen, and to do that with plasma would require a significant amount of research.

We spoke to Panasonic about 4K on plasmas when it demoed its final run of plasma TVs to us. The firm told us that 4K was impractical on plasmas for a few reasons, but power-draw was something of a hurdle that would require a lot of work to overcome. It’s worth remembering that environmental legislation has changed a lot since plasma TVs were first sold: if you tried to develop a tech that power-hungry now, you’d never be allowed to sell it in most of the world.

The second, and more critical, issue comes down to the miniaturisation of the plasma cells. It’s possible to create a plasma TV with a 4K resolution screen – we know this because Panasonic sells a 152in 4K plasma screen. Sadly, it’s the miniaturisation of plasma cells that creates a very real issue for practical 4K screens. Most domestic 4K TVs will be 50 to 85in in size, it’s possible you could make plasma cells small enough to produce 4K on 85in, but that would be a challenge. Also, even if the plasma cells could be shrunk significantly enough to fit 4K resolution on a practical-size screen, the level of brightness would be severely compromised.

The gradual move to 4K has meant that companies like Samsung, Panasonic and LG are all looking at their options. While they all sold plasmas, Panasonic and Samsung have announced that they will no longer manufacture plasma TVs. As of now, LG is the only company that has hinted plasma has any future at all. But however you look at it, in a 4K world, plasma’s time is limited.

Should I buy a plasma TV then?

Despite the fact that plasma production is winding down, the technology remains incredible. People who care about picture quality will generally prefer the way plasma TVs look on 1080p material. Get a good plasma TV, and you’ll have a picture that has beautiful black levels, amazing colour and a cinematic look that makes movies feel like a real cinema experience.

There are plenty of plasmas with 3D capabilities, indeed virtually all of them will have 3D along with smart functionality to stream video and other media to your TV. Those smart functions will also give you access to apps, games and selected Internet content, like YouTube and video podcasts.

There is no reason to worry, and plenty of reasons to get excited about buying a new plasma TV, especially since you might be able to negotiate quite a bargain while the masses opt for LED screens instead.