Temporal Light Modulation in OLED Displays

Many OLED displays, including those in modern smartphones, control brightness through a combination of continuous dimming and PWM dimming. Continuous dimming, or DC-dimming, is achieved by adjusting how brightly pixels are illuminated directly, and doesn't produce flicker. However, most OLED displays are only capable of DC-dimming to a moderate brightness level. DC-dimming below this level would cause issues with color accuracy and minimum current requirements. To reach lower brightness levels, PWM based dimming is typically used. PWM adjusts brightness by turning off the pixels for a portion of each frame.

It is important to note that OLED displays typically update one row at a time. This update process creates some amount of flicker even on full brightness settings. The visualizations below are designed to help understand OLED scanning and proper measurement.

The visualizations below are general and apply to many, but not all, OLED devices. They most closely model iPhone OLEDs, such as those on the iPhone 16 and iPhone 17.

How OLED Rows Scan

Each row of an OLED display is driven sequentially, offset in time by fraction of the refresh period. Drag the brightness slider to see how the panel switches between DC dimming (above 50%) and PWM dimming (below 50%). This is what your eyes and brain are responding to when you view a typical OLED, although the flicker is not visible to the naked eye.

How Distance Affects the Measured Waveform

This visualization shows how a flicker meter will measure an OLED like the one in the previous visualization. As a sensor moves away from the screen, it captures light from more rows at once. Since each row fires at a slightly different moment, this blurs the PWM waveform — reducing the measured flicker depth. The blue curve shows what the sensor sees; the faint line is the true single-row signal.

This visualization should not be taken to mean that moving further from your OLED screen will reduce perceived flicker. Unlike a sensor, your eye does not average the rows of pixels on the screen: it forms an image.

When measuring flicker from OLEDs, we should aim to capture only light from a few closely spaced rows. Even a few millimeters of distance can lead to inaccurate measurements. One technique is to mask off the majority of the rows of the display (with tape or cardboard) and place the sensor as close as possible to the visible rows.