The difference between these displays is the dynamic refresh rate of up to 120 Hz. Moreover, Apple only equips its flagships with these screens, starting from the iPhone 13 Pro and 13 Pro Max. All base models now come with standard 60Hz OLED displays. As a result, the company will move away from this practice with the iPhone 17 series.
Thanks to energy-saving technologies, battery power is saved and the iPhone’s battery life is increased: the refresh rate is reduced to 1 to 10 Hz instead of 60 Hz, depending on the model. This allows you to use the Always On Display function at all times, with the clock and notifications displayed on the lock screen, even when the device is in sleep mode.
Source: Ferra

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