The scope capture is able to show the difference between using a resistor or constant current regulator(CCR). Both are applied a rectified 60hz AC signal. Because of Ohms law, the resistor will only change the amplitude of the current applied to the led. It tracks the input voltage and produces an output that matches the voltage waveform. The CCR is able to provide a constant current over a range of input voltage. This is shown on the right side of the picture. The current regulation creates a flat stable light output when the input voltage is above a certain threshold. It cannot correct for low voltages in the signal since it does not contain any energy storage devices. Though better than a resistor, there is still significant flicker at 120hz.