Are AMOLED displays at risk of burn-in?
According to the calendar on my office wall, it’s 2014. However, the phone on my desk suggests I’m stuck in the 1980s. What’s going on? Am I in an episode of Ashes to Ashes? No – what has prompted my mental flashback is screen burn.
Anyone old enough to remember the big, bulky CRT monitors we used back in the day – especially the pre-colour, green-screen VDUs – may remember the phenomenon that Americans refer to as “burn-in”.
Continuously displaying a particular pattern, logo, icon or even just the OS command prompt in the same place could damage the phosphor coating behind the screen’s surface to the extent that it left behind a permanent “ghost” image.
Anyone old enough to remember the big, bulky CRT monitors we used back in the day may remember the phenomenon that Americans refer to as burn-in
Much like the efficiency of fluorescent light tubes fades over time, the efficiency of a cathode ray tube’s phosphor coating decreases slightly every time it’s used, so if one place on the screen was constantly lit, that image was permanently burned into the light-emitting surface. I remember almost crying the first time this happened to one of my very expensive first-generation Sony SVGA monitors.
Fortunately, many of us have forgotten about this effect, since modern LCD panels aren’t subject to it. Strangely, however, some monitors and TVs still include in their circuitry or firmware various tricks to combat screen burn, such as detecting images with constant areas and shifting offending images by a pixel or two in random directions; I’ve no idea why their makers still feel the need for this precaution, since screen burn is a thing of the past, isn’t it? Regrettably, this isn’t the case.
If you look at the phones and tablets on sale on the high street and examine their specifications carefully, you’ll notice that screens come in two forms: IPS (which stands for in-plane switching) and AMOLED (active-matrix organic light-emitting diode).
In their most basic forms, IPS technology employs a backlight sited behind a variation on a traditional LCD panel, while an AMOLED display is composed of organic LEDs that are themselves light-emitting. There are various types of both technologies, such as Samsung’s Super PLS (plane-to-line switching) and Super AMOLED Plus, but the underlying technology is largely the same.
In terms of currently popular phones, Samsung tends to use AMOLED panels on its phones, as do Nokia and Motorola, while Apple is sometime criticised for using IPS – an “older” technology – in its devices. But is such criticism fair?
In fact, both types of screen have pros and cons. IPS displays have better colour accuracy, and they’re capable of showing whiter whites. On the downside, they can be more power-hungry than AMOLEDs, which can also be made thinner, since no backlight is required.
The blacks are better on an AMOLED screen, since its pixels are turned off and emit no light; IPS black pixels merely attempt to block the backlight, with only partial success. AMOLED screens aren’t as sharp as IPS panels, however, and can be more difficult to read in bright sunlight. To my mind, however, the biggest problem with AMOLED displays is that they suffer from screen burn.
The “O” in AMOLED
The problem is the “O” in the AMOLED acronym, which stands for “organic”. The organic compounds used in AMOLED displays are polymers or copolymers, such as polyfluorene (PFO) and polyphenylene vinylene (PPV), both of which degrade with use.
This is partly due to the fact that the chemistry involved in creating the electroluminescence is irreversible, so the luminous pixels degrade as they’re used up, like a battery. These organic materials tend to crystallise, too – an effect that is exacerbated at higher temperatures. That’s something to bear in mind the next time your phone becomes warm while you’re playing a game or watching a video.
There are two main types of AMOLED display. Some have traditional RGB stripe layouts, such as those you’ll find on an LCD monitor, which use three subpixels per pixel. Others have a PenTile layout that employs a two-subpixel layout of red-green and blue-green pairs.
As a result of this structure, PenTile screens contain twice as many green subpixels as reds and blues, and since it’s the blue subpixels that degrade most quickly, PenTile displays are less susceptible to screen burn than the RGB type of AMOLED screens.
Incidentally, PenTile is a patented matrix layout owned by Samsung, although there are other manufacturers that have licensed it.
So, how does this screen degradation affect a typical smartphone or tablet user? Well, if you leave your AMOLED screen turned on while charging – which is one of the options in the Android settings screen – within a few weeks you’ll see faint images of the icons appear on your homescreen, with the Android soft keys burned into your display.
In day-to-day use, this might not be noticeable, but if you’re looking at screens with a white background – when using a minimalist word processor, for example – you’ll spot yellow/brown marks on the display. It isn’t merely leaving the screen on while charging that causes the problem, either: items such as car cradles, docking stands and even satnav apps are troublesome, too.
This isn’t an issue you’d expect to encounter in a top-of-the-range device for which you may have paid hundreds of pounds, yet it’s a problem that’s rarely mentioned. When was the last time you read a phone review that covered the possibility of screen burn? Or when was the last time you saw phone packaging or a user manual that warned you that the screen technology used in the device makes it susceptible to screen burn?
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 switched on for long periods. So readers, please spread the word.