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iPhone X Eye Strain: How to Stop OLED Flickering in Just Three Clicks

March 5th, 2018 by Oleg Afonin
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The iPhone X uses a new (for Apple) display technology. For the first time ever, Apple went with an OLED display instead of the IPS panels used in all other iPhones. While OLED displays have numerous benefits such as the true blacks and wide color gamut, the majority of OLED displays (particularly those made by Samsung) tend to flicker. The flickering is particularly visible at low brightness levels, causing eyestrain and headaches to sensitive users. Very few users have the slightest idea of what’s going on, attributing these health issues to oversaturated colors, the oh-so-harmful blue light and anything but OLED flickering.

So let us have a look at what OLED flickering is and how to get rid of it on the iPhone X for much better low-light readability.

OLED Flickering: PWM Controls Brightness

The flickering of OLED displays has to do with the way the phone dims screen brightness. There are several techniques that can be used to dim the screen.

The backlight brightness (in LCD displays) or the brightness of individual light-emitting diodes (in OLED panels) can be altered by applying different levels of voltage to the light-emitting diodes. There is also an alternative way to control backlight brightness by simply cycling the backlight on and off in rapid succession. This method is called Pulse Width Modulation (PWM). While this backlight cycling is supposed to be undetectable to the human eye, a large number of users does notice the PWM effect as screen flickering. An even larger group of users experiences eyestrain and headaches because of such cycling without consciously noticing any flickering. The issue is explained in more details in this article: Pulse-width modulation (PWM) in OLED displays. One picture shows it all:

(Source: OLED-info)

As you can see, at low brightness levels the OLED panel periodically emits pulses of bright light to make the screen appear dimmer. This, and not oversaturated colors or the “blue light”, is the real cause of strain and headaches associated with OLED displays.

The issue is particularly pronounced in low ambient brightness levels. In dark environments, your pupils get bigger (dilate), allowing more light to pass to your retina. The pulses of bright light pass through your dilated pupils and bombard your retina, causing severe eyestrain even if your brain does not consciously notices the pulses.

OLED Displays Without Flickering

Manufacturers apply different diming techniques to control brightness of their OLED displays. Very few OLED displays have zero flickering; the only example known so far is the P-OLED panel installed in LG G Flex 2 back in 2015. While getting away from the flickering was good for your health, the image quality suffered. At low brightness levels, the display of the LG G Flex 2 could look like this:

Why does that happen? The reason is manufacturing tolerances. While adjacent organic LEDs emit similar amounts of light at high voltage levels, at lower voltages, where fewer photons are emitted per diode, the variance of parameters between adjacent dots takes its toll. In a way, this is similar to digital camera noise. While the image looks great at bright daylight, images captured in dark environments with fast shutter speed (and high ISO levels) will have a certain amount of digital noise.

To mitigate this issue, some manufacturers opt to always apply the highest possible current to their OLED panels. Such displays look great in tests and win multiple awards for image uniformity among other things. However, these OLED panels flicker at all brightness levels. Phones using such panels include Samsung Galaxy S6, S7, S8, S9, Microsoft Lumia 950, Motorola Moto Z and a number of others.

Other manufacturers are not happy about the constant flickering, opting for hybrid approach to dimming screen brightness. Phones such as the Moto Z2 Play, ZUK Z2, Nexus 6, OnePlus 5, and iPhone X use OLED panels that won’t flicker beyond a certain brightness level. OLED panels used in these devices will dim to about 15-35% of maximum brightness by lowering the current (thus no flickering). PWM is applied to further dim the screen. Compared to the first group of devices using PWM all the way up to 100% brightness, these devices exhibit visibly less flickering due to the lower pulse amplitude.

This is how the iPhone X dims its screen brightness:

Source: iXBT

German reviewers checked for PWM using an oscilloscope. It looks like this:

As you can see, there is no PWM flickering at 50% brightness level. At 25% brightness, there is strong PWM flickering.

How to Check for PWM Flickering

What if your eyes are not sensitive enough to see PWM flickering? It is easy to check whether your phone has it by using another phone’s camera. Just bring your iPhone X to a dark place, open an app with predominantly white background, and set the iPhone to minimum brightness. Then point your other phone’s camera onto the iPhone screen. You will see something like this:

 

Hint: pointing Safari to “about:blank” will open a white page.

Now pull the Control Center on the iPhone and start increasing its brightness. Look at its display through the other phone’s camera. At some point, the stripes are gone. This means you’ve reached the PWM-free level of brightness.

Now, if we were to keep the iPhone X at this level of brightness, its display would be completely PWM-free. The problem, however, is that the minimum PWM-free level of brightness on the iPhone is much too bright for dark environments. In order to put brightness down to comfortable levels, we’ll need to apply a dark filter covering 100% of the screen. In iOS 11, you can do it by opening the Settings app and looking up Display Accomodations under Accessibility.

Under Display Accomodations, activate Reduce White Point by tapping the check box. Now, tap the Reduce White Point label outside of the check box and configure Reduce White Point as shown on the screen shot. (Hint: adjust the slider to your liking. We found values between 85 to 100% to work great for reducing PWM in dark environments).

Three Clicks to Enable PWM-Free Display

Once you set the brightness slider to PWM-free level (somewhere around 50% brightness), your iPhone X OLED display will become PWM free at effective brightness that are comfortable for dark environments. But what about bright ambient lighting? You won’t want to have this screen filter on at all times, just in the dark!

No worries, Apple has another option for you to make switching the filter on or off as easy as tapping the Sleep/Wake button three times. Search Settings for “Accessibility Shortcut”, enable and configure it to invoke “Reduce White Point” as shown on the screen shots below.

That is it! Now, with three clicks of the side button you will instantly turn on and turn off the dimmer, making your iPhone X OLED screen effectively PWM-free in all lighting conditions. Just make sure to adjust the brightness slider to the last PWM-free level while keeping screen brightness at comfortable levels!

More Information

If you’re interested in PWM and how it affects users, we’ve assembled a collection of links and discussions.

The iPhone X is using AMOLED, so what is the PWM frequency?

iPhone X has PWM with 240Hz

Eye-strain while using iPhone X

Pulse-width modulation (PWM) in OLED displays

OLED eye strain and migraines


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