Paul Ockenden revisits a screen damage problem from the past.
I just glanced up at the calendar on my office wall and it said 2016. Then I glanced down at the phone on my desk and suddenly it was the 1980s all over again.Why? Has this column suddenly turned into an episode of the BBC's Ashes to Ashes? No, the reason for my mental journey back to the ‘80s was screen burn. Anyone old enough to remember the big and bulky CRT monitors we had back then (especially the pre-colour green screen VDUs) will probably recall the phenomenon of screen burn, or burn-in as the Americans liked to call it. It was when the constant display of a particular thing (a pattern, a logo, an icon, or even a command prompt) damaged the phosphor used to coat the surface of the screen causing a ‘ghost’ of the image to be permanently displayed.
I’m sure everyone is aware of how the efficiency of a fluorescent light tube will fade over time – well, exactly the same is true of cathode ray tubes. The efficiency of the phosphor coating behind the glass at the front of the screen decreases with usage, and if a particular part of the screen is constantly lit-up the image is permanently ‘burned’ into this light emitting part of the screen. I remember almost crying the first time this happened to one of my very expensive first generation Sony SVGA monitors.
It’s an effect that many of us have now, thankfully, forgotten about because modern LCD displays aren’t subject to the same effect (although, strangely, some monitors and TVs do still include the various tricks used to combat screen burn in their circuitry or firmware, particularly detecting an image with a constant part – such as an on-screen logo – and then shifting the image a pixel or two in a random direction now and again). I've no idea why LCD screens still feel the need to do this.
So screen burn is a thing of the pant then? Unfortunately not. If you look at the phones and tablets on sale in the high street – actually who am I kidding? Nobody buys tech in the high street any more. If you look at the phones and tablets on sale in one of the big out-of-town technology sheds, or perhaps your local global-mega-hyper-mart, and if you look carefully at the specifications listed on the shelf tickets, you’ll notice that the screens come in two basic flavours, IPS (standing for In-Plane Switching) and AMOLED (the acronym breakdown of which we'll come to in a moment). IPS uses a backlight behind a variation on the traditional LCD panel, AMOLED on the other hand is a light emitting panel of organic LEDs. There are various flavours of both technologies, such as Samsung’s Super PLS (a type of IPS), and Super AMOLED Plus, but the underlying technology is pretty much the same in all cases.
In terms of currently popular phones, Samsung tends to use AMOLED panels on most of its phones, and it's becoming increasingly popular elsewhere. Apple uses IPS screens, although it is sometimes criticised for using an ‘older’ technology in its devices. But is this criticism fair?
Both types of screens have their pros and cons. IPS displays have better colour accuracy, and in particular are capable of showing whiter whites. On the downside, though, they can be quite power hungry. AMOLED screens are much kinder on the battery, and can be thinner because there’s no backlight required. The blacks are better with AMOLED screens too, because the pixels are actually turned off, rather than black pixels being formed by trying to obscure the backlight. The screens aren’t as sharp though, and can be harder to read in bright sunlight. To my mind, though, the biggest problem with AMOLED displays is that they bring back that long-forgotten problem of screen burn.
The problem is the O in the AMOLED acronym – It stands for Active-Matrix Organic Light-Emitting Diode. The organic compounds used in AMOLED displays, substances such as polyphenylene vinylene (more commonly known as PPV) or Polyfluorene (PFO) polymers or co-polymers, can all degrade with use. This is caused by a number of factors, firstly because, at least in part, the chemistry involved in the electroluminescence process is irreversible, so just like with a battery the devices will degrade as they are used. Secondly, the organic materials tend to crystallise, an effect which can be exacerbated at higher temperatures. Something to remember next time your phone gets warm while you are playing a game or watching a video.
There are two main types of AMOLED displays, some with traditional RGB stripe layouts like you'll find on an LCD monitor (using three subpixels per pixel), others having a PenTile layout which uses a two subpixel layout or red-green and blue-green. Because of this structure PenTile screens have twice as many green subpixels, and fewer red and blue subpixels. It’s the blue subpixels which degrade most quickly, so as a result PenTile displays are a bit less susceptible to screen burn than other AMOLED displays, but they are still vulnerable.
Incidentally, PenTile is a patented matrix layout, owned by Samsung, although some other manufacturers have licensed it. Knock-off clones don't seem to be much of a problem, although that's perhaps not surprising given the highly litigious nature of the mobile devices marketplace.
So how does this degradation affect a typical smartphone or tablet user? Well, if you leave your AMOLED screen on when charging, for example (it’s one of the options available in the Android settings screen), after a few weeks you’ll find things like the icons on your home screen and the Android soft keys burned into your display. In normal day to day use this burn might not be noticeable – at least, not until it starts to get really bad. But if you’re looking at a screen with a blank white background – using one of the minimum chrome word processors for example – you’ll notice some yellow/brown marks on the screen.
It’s not only leaving the screen on while charging – things like car cradles, docking stands, and even SatNav applications can all cause the same problem.
It’s very annoying, especially when you’ve paid hundreds of pounds for the latest top of the range phone, and yet it’s a problem that hardly ever gets talked about. When was the last time you saw a phone review where it mentioned the possibility of screen burn? When was the last time you saw phone packaging or a user manual which warned that the particular screen technology used in the device made it susceptible to screen burn problems? Probably never. I think it’s an issue that needs much greater publicity – consumers need to be told about the relative fragility of AMOLED displays, and that such phones and tablets shouldn’t be left with their screens on for long periods of time. So, readers of the Real World, please spread the word!
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