Key Takeaways
1. Most OLED screens in smartphones use pulse-width modulation (PWM) for power control, which can cause discomfort for sensitive individuals due to low frequencies.
2. Apple has introduced a feature called Display Pulse Smoothing in the iPhone 17, allowing users to disable PWM dimming, but it is limited to brightness levels up to 25%.
3. Above 25% brightness, the iPhone 17 still relies on PWM dimming, and the effectiveness of the new feature remains uncertain.
4. YouTuber Nick Sutrich suggests Apple may be using pulse amplitude modulation (PAM) for smoother brightness transitions, but specifics are not confirmed.
5. Users sensitive to PWM report continued discomfort even with Display Pulse Smoothing activated, indicating limited relief from the new feature.
Most OLED screens found in today’s smartphones utilize a technique known as pulse-width modulation (PWM). This technique controls the average power of an electrical signal by rapidly toggling the screen on and off. PWM can be implemented in a way that is more precise, energy-saving, and cost-effective compared to analog methods.
The Issue with PWM
The downside to PWM is its typically low frequencies, often under 500 Hz. People who are sensitive to flickering may notice this and could experience discomfort like burning eyes, headaches, and nausea, among other symptoms.
Apple’s New Solution
It is therefore a positive development that Apple has introduced an option to disable PWM dimming in its latest iPhones, including the Apple iPhone 17. This feature, called Display Pulse Smoothing, can be found in iOS 26 under Settings, Accessibility, and Display & Text Size.
Limitations of the PWM Option
However, as shown in our review of the Apple iPhone 17, users shouldn’t have high expectations for this PWM feature. It only functions effectively at screen brightness levels up to 25%, and the dimming frequency remains unchanged. Above 25% brightness, the device still relies on PWM dimming.
Apple vaguely describes the activation of display pulse smoothing as an “alternative method for dimming the OLED display.” While it is suspected that the company employs a form of DC dimming or a hybrid approach, no specific technical information is provided.
Insights from YouTuber Nick Sutrich
In a video, YouTuber Nick Sutrich suggests that Apple might be using pulse amplitude modulation (PAM) for the display pulse smoothing feature. PAM differs from PWM by altering the signal amplitude, or voltage level, which creates a sine wave-like signal curve rather than a square wave, leading to smoother transitions in brightness.
Measurement Observations
Our measurements support this effect. When display pulse smoothing is enabled, the frequency response appears significantly flatter at brightness levels up to 25%.
Despite the method employed, it seems that the new feature provides little relief for those sensitive to PWM. Numerous users on the Reddit forum r/PWM_Sensitive have reported that even with this dimming option activated, they still suffer from the same symptoms associated with traditional PWM dimming.
Conclusion
The reasons for the limited effectiveness of the display pulse smoothing option seem to stem from the unchanged dimming frequency and modulation rate in comparison to PWM dimming—these factors are significant contributors to the symptoms experienced by users.
While it’s commendable that Apple has introduced a PWM option in its latest iPhone models, it remains unclear if this feature will be more effective in the future and truly assist PWM-sensitive users. Let’s hope that improvements come soon through a software update rather than waiting for the next generation of devices.
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