The easiest way to test for bad PWM is to sit in a full dark place, and turn the light onto the various modes.
Then wave your fingers, or a pencil, white stick, etc. as fast as you can through the beam.
Good PWM or no PWM you’ll see, the stick waving in the beam.
Crappy PWM will show the stick looking like an old time movie, jerky movements, with sharp moments and blur.
If you can see this, usually the PWM is poor enough to be bothersome.
Also videoing the beam shining in a dark room will show – some – PWM. The PWM frequency will interact with the shutter of the camera and the video will show the light pulsing.
Or use a camera, open the shutter for a half second, and swing the light through the frame as fast as you can.
And example. Nitecore TUBE 500Hz PWM.
So you are capturing a light that is flashing on for a brief time 500 times a second.
Looking at the PWM on a scope shows
The light is on for only a very short period during the 1/500 of a second cycle.
A light with slow PWM will show as a series of pulses instead of a steady beam.
You can detect PWM up to around 4K with this method (If you can wave your arm fast enough).
I describe how to measure PWM using a sound card in this thread.
All the Best,
Jeff