OLED - The good, the bad and the ugly / by Erik N

Introduction

 Closeup of LCD display

Closeup of LCD display

To better understand the advantages and disadvantages of OLED displays, we need to take a brief look at LCD displays. The way LCD displays work is that they have a backlight that’s always emitting white light through color filters. Each pixel consists of three subpixels which are red, green and blue. To change the color of a pixel, LCD crystals control how much light goes through each of these individual subpixels to mix the desired color.

 Closeup of AMOLED display

Closeup of AMOLED display

OLED displays does things differently. Instead of each subpixel being a color filter regulating how much of the backlight is let through, each subpixel of an OLED display is it’s own LED light source. The intensity of each subpixel is what determines the color of light emitted by a pixel.

 

The good

By having the subpixels being their own lightsource, the backlight is eliminated. This allows for thinner display panels, flexible display panels, and lower power consumption. If 50% of the display is showing black, those 50% is consuming no power. It also allows for more vibrant and accurate colors, and better constrast. Unlike LCD, black is truly black. The black pixels aren’t lit at all, whereas the LCD will still have the backlight on for the entire display and some light will leak though. Black on an LCD is more like very very dark gray. The viewing angles are also better. Because of the better contrast they are suitable for HDR viewing.

The thinner panels allow for either a thinner device, or room for more of other things, like bigger batteries or more electronics. There are however LCD technologies like "Pixel Eyes™" by JDI that allows for thinner LCD panels as well.

 

The bad

OLED panels have a shorter lifespan than LCD panels. As evident by the name (Organic Light Emitting Diode) they use an organic compound. This compound breaks down over time. This can be seen as ”burn in” effects that isn’t technically an image burned in, but rather uneven ageing. It’s better described as permanent image retention. The blue subpixels age quicker as blue light contains more energy. This gives the display a yellow tint that increases over time. This can be mitigated by calibration in devices where this is possible, and our vision compensates well for this so it can be hard to notice without a truly white reference. The bigger problem is the uneven aging across the display. For example, areas which show more blue light age quicker than areas that show less. This can eventually be seen as parts of the user interface leaving faint images even when not shown, something that is most evident when displaying a light gray image. The ageing problem is improving constantly as OLED research progresses, so it may not be a big problem in the future.

Manufacturers also know about the longevity problem, and Apple has a support document outlining how to get the most out of their iPhone X Super Retina display. They recommend using auto brightness, using a short duration for auto lock, avoiding to display static images at maximum brightness for long periods of time and to turn brightness down if using an app that keeps the display on. The latter could for example be navigation apps. In other words, to keep the display in a good condition, some effort is needed on the users part.

The other big problem is cost. OLED panels are still expensive and relatively difficult to make well. That’s why we don’t se many laptops and TV’s with OLED displays yet, and those that exist tend to be very expensive. This will likely improve as production scales up to meet demand.

 

The ugly

There is a not insignificant part of the population that are sensitive to flickering light. I have heard numbers of around 10%. I am one of those people. OLED displays use PWM (Pulse Width Modulation) to adjust the intensity of the pixels, which makes the displays flicker. Most OLED equipped phones run PWM at a frequency of around 250 Hz. This is high enough not to be visible to the naked eye, but still low enough to be detected by the brain. Symptoms in those affected are things such as motion sickness, eye strain, headaches and migraines. The symptoms can set in right away, or can increase in intensity over time.

This means that this group of the population can’t use OLED equipped devices without experiencing mild to severe discomfort and pain. Something that is becoming a bigger and bigger problem now that everyone, including manufacturers, seem to be in some sort of OLED craze. If a phone does not have an OLED display, reviewers and some tech enthusiast consumers tend to complain while those of us who can’t use OLED devices applaud. This is not only a problem with OLED but with LED dimming in general. Modern LCD panels use analog dimming, which is flicker free, or at least use PWM with very high frequencies of several tens of thousands of hertz. LED light bulbs though, tend to heavily use PWM. Especially the dimmable ones.

An excellent resource to see what devices use PWM is the PWM Ranking by Notebookcheck.net, which can be found here: https://www.notebookcheck.net/PWM-Ranking-Notebooks-Smartphones-and-Tablets-with-PWM.163979.0.html

 

The future

In terms of longevity, OLED displays continue to improve as more research is done. There is also research being done on MicroLED displays, which would omit the organic compound.

As for the PWM and flickering, I hope work is being done to improve the situation. I used to have trouble finding displays I could tolerate when LCD computer displays first came out, and then also with early smartphones, but around 2012-2013 the situation improved with analog dimming taking over. I could chose the device I wanted rather than the device I could tolerate which was great. Now choise is becoming very limited again as OLED displays find their way into everything.

I hope for the sake of those of us that are sensitive to flickering that manufacturers and researchers take this issue seriously. 10% is a not insignificant part of the population. And who knows if the flickering may have a health effect on those who don’t experience clear symptoms. That last thing is of course just speculation on my part.

 

Conclusion

Knowing all of this, I believe that OLED is not yet a technology mature enough for widespread adoption. In my mind the drawbacks outweigh the benefits. With lifespan issues and causing health issues for a large part of the population I think adoption should be much more conservative until these issues are solved. The lifespan problem is likely to affect the environment as well if devices won’t last as long. It may not be a problem to the user for the first two or three years but some keep their phones for 4-5 years, or buy phones used, and products such as TV’s should last much longer, preferably 10+ years.

I do acknowledge the benefits of OLED though, and if the problems with longevity and flicker can be solved I’m all in. It is in many ways a superior technology currently hampered by some significant drawbacks.

 

Bonus

Here are two closeups of a photograph of a street light, first shown on an OLED display, then on an LCD display. The different scales are due to differences in pixel density, with the OLED display at ~316 PPI, and the LCD at ~122 PPI.