I find that the easiest and maybe cheapest way to measure PWM is to use a digital camera with 4000 or even 8000 shutter speed and take video with a fast lens, e.g. F 2.0 so there is enough light even when measuring quite dim screens.
I have been able to measure PWM in the several Khz with this method. Mathces what Notebookcheck.com meausres.
I see no reason to have an expensive oscilloscope.
Also for the older post - fluorescent light flicker either 120 or 100 Hz based on the electricity frequency. Fluorescent lights also dim and light slowlly in comparison toe LED, so the flicker is not really that abrubt.