iPhone Xs PWM Demystified: How to Reduce Eyestrain by Disabling iPhone Xs and Xs Max Display Flicker

October 30th, 2018 by Oleg Afonin
Category: «Did you know that...?», «Hardware», «Tips & Tricks»

The iPhone Xs employs a revised version of the OLED panel we’ve seen in last year’s iPhone X. The iPhone Xs Max uses a larger, higher-resolution version of the panel. Both panels feature higher peak brightness compared to the OLED panel Apple used in the iPhone X. While OLED displays are thinner and more power-efficient compared to their IPS counterparts, most OLED displays (including those installed in the iPhone Xs and Xs max) will flicker at lower brightness levels. The screen flickering is particularly visible in low ambient brightness conditions, and may cause eyestrain with sensitive users. The OLED flickering issue is still mostly unheard of by most consumers. In this article we will demystify OLED display flickering and provide a step by step instruction on how to conveniently disable (and re-enable) PWM flickering on iPhone Xs and Xs Max displays to reduce eyestrain.

OLED Technology: PWM Brightness Control

Unlike IPS, most OLED panels use a different method for controlling their brightness. At certain brightness levels, dimming the screen is achieved by controlling voltage applied to the individual light-emitting diodes. However, manufacturing tolerances available with today’s OLED technologies are only sufficient to maintain brightness uniformity between adjacent light-emitting diodes within a limited voltage range. At lover voltages, the differences between individual light-emitting diodes start showing up, and instead of solid grey you get a panel that may look like this:

The image above shows the display of the LG G Flex 2 at minimum brightness. This phone used an OLED display without PWM and without flickering; the drawback is clearly visible.

To combat this issue, manufacturers had to resort to an alternative method of brightness control. This method is called Pulse Width Modulation (PWM), and uses short bursts of bright light to create an illusion of a lower-lit image. The bursts occur at frequencies that are supposed to be imperceptible by most users. However, a large group of people does notice the flickering caused by PWM, and an even larger number of users experiences eyestrain and headaches without being consciously aware of the flickering. The issue is explained in more details in this article: Pulse-width modulation (PWM) in OLED displays. This is how PWM brightness control may look:

(Source: OLED-info)

The flickering issue is particularly dangerous at low ambient brightness. Once your pupils dilate, they allow more light to pass to your retina. The short bursts of bright light pass through your dilated pupils and cause eyestrain even if your brain does not consciously notices the pulses.

What Apple Does About PWM Flickering

Samsung, the largest manufacturer or AMOLED displays, is among the worst offenders, always applying high voltage to light-emitting diodes. At lower brightness levels this results in very short bursts of extremely bright light; PWM flickering at its worst. Many Samsung phones flicker at all brightness levels except when they are at a 100% level. This, for example, is how iXBT measured PWM flickering of the Samsung Galaxy Note 8:

Compared to Samsung devices, Apple uses a really modest level of PWM control, trying to avoid short bursts of bright light at 50% and above levels of brightness. This is how iXBT measured PWM flickering of the iPhone Xs Max:

Compared to Samsung phones, the iPhone Xs (and Xs Max) only resort to PWM-based control at very low levels of brightness. The iPhone Xs and iPhone Xs Max display backlight flickers at 240 Hz at a brightness setting of 50% and below. There is no visible PWM flickering above the 50% brightness setting. Sensitive users may opt for the iPhone Xr that uses an IPS display without PWM.

In this YouTube video submitted by ScoGee you can see how PWM kicks in at 50% brightness and below:

Looks pretty severe? We have good news for you: you can mostly avoid PWM flickering on the iPhone Xs and iPhone Xs Max by following two simple steps.

Step 1: Using iOS Display Accommodations to Reduce PWM Flickering

In order to reduce PWM flickering on the iPhone Xs and iPhone Xs Max, we’ll use a feature of iOS called “Display Accommodations > Reduce White Point”. This feature dims the maximum brightness by applying a dark filter over the display. Once you enable Reduce White Point, the brightness of whites and bright colors will be dimmed.

If you were using an iPhone or iPad equipped with an IPS display, the physical level of backlight would remain stable, but visible brightness would be reduced. On the IPS display, using Reduce White Point would cause higher power consumption, reduce visible contrast and produce dull colors. There are no such effects on OLED-equipped devices since there is no backlight in the first place. OLED panels have infinite contrast and wide color gamut, so reducing white point does not have much effect on the contrast or colors. If physical brightness of your iPhone Xs or Xs Max display remains at 50% setting or higher, there will be no PWM flickering either; the Reduce White Point filter will, however, dim the display to acceptably low levels. In other words, activating Reduce White Point provides a much more pleasant visual experience in low ambient light.

Activating Reduce White Point requires the following steps:

Launch Settings from your Home screen

Tap General > Accessibility

Tap Display Accommodations

Tap the switch next to Reduce White Point

Drag the slider to your preferred setting. A good starting point for the iPhone Xs and iPhone Xs Max is 95%. For stronger dimming effect (to be used in extreme darkness) use 100%.

Finally, pull down the Control Panel of the iPhone and set the Brightness slider to the 50% setting or above. This ensures that there is no visible flickering.

If you have to drag the Brightness slider to a setting lower than 50%, you will start seeing some flickering. If this is the case, go back to Display Accommodations and increase the value of Reduce White Point. In extreme darkness, set the filter of Reduce White Point to 100%.

Step 2: Use Shortcuts to Quickly Disable and Re-Enabling PWM Flickering

After successfully completing the first step, you have reduced the white point of your display significantly. This in turn means that while your display looks great (and is flicker-free) in low ambient light, it will look very dim outdoors. At this point, you’ll want a way to quickly disable Reduce White Point without going through the Settings app.

In order to quickly control PWM, you will need to create an Accessibility Shortcut.

First, search through the Settings app for “Accessibility Shortcut”, or go directly to Settings > General > Accessibility and scroll all the way down.

Tap Accessibility Shortcut, then select Reduce White Point as shown below.

This toggles the Reduce White Point with a triple-click of the side button (the Sleep/Wake button), dimming your screen to make your iPhone Xs or Xs Max effectively PWM-free. Another triple-click of the side button, and your display is back to its normal brightness.

Step 3: Use Control Center to Control PWM Flickering

iOS 12 brought an additional way of controlling PWM flickering through Control Center via Accessibility shortcuts. You can use this method to add an icon to your iPhone Xs or Xs Max Control Panel in addition to the power button trick.

To add the Accessibility shortcut to your Control Center, you will need to customize Control Center by following these steps.

Open the Settings app and locate Control Center (just under General).

Tap Control Center > Customize Controls.

The Accessibility Shortcuts icon should be available under More Controls. Tap next to Accessibility Shortcuts.

The Accessibility Shortcuts icon will be added to the list of controls.

Pull down the Control Center to verify that the shortcut has been added. You may adjust the position of the Accessibility Shortcuts icon in your Control Center by dragging it up and down in the Control Center Settings.

To activate the accessibility feature from the Control Center, pull down the Control Center, then tap the Accessibility Shortcuts icon.

Congratulations! You can now quickly enable and disable dimming of the iPhone Xs or Xs Max display via Control Center.