Seagull I wonder if the test equipment used to make pwm graphs isn't sensitive enough to capture just how sharply LEDs/OLEDs can illuminate, given than an LEDs could illuminate about ten times faster than these graphs show.
It's probably fast enough. At 60 Hz, which is a very slow frequency, any cheap equipment such as our current 100K resistor method (see oscilloscope thread) should be fast enough to show true rectangles if the source signal is rectangular. I got a similar signal on the OnePlus 3. You'd start to see curves at frequencies like several kilohertz but not 60 Hz. The curves we see on the picture most probably happen like the picture indicates. It's interesting though that the spikes become largest when placing the sensor directly on the surface (seen during my own tests). The flicker might run from like top left to lower right corner, which could be an explanation. With 2 sensors at once and overlapping graphs, one could probably prove that. Most oscilloscopes have at least 2 inputs. I currently don't have a working oscilloscope setup but maybe someone else would want to try it.