Based on this question - Two pictures with the same setting come out with different lighting - and the answers & comments I did a quick test on one of my LED continuous lighting panels.
I'm aware of the potential for flicker on LEDs, as with fluorescents etc but I realised I'd never noticed it when shooting using only two of these panels. They're Excelvan GK-J-1040AS which I admit I just found on eBay the same time I bought my first DSLR last November before I knew anything about the subject at all, so let's call it a fairly random newbie choice.
I did a quick test on a lit subject, trying faster & faster exposure, to see if I could catch it 'in between' pulses... but I couldn't.
As a final test I rather uncomfortably pointed the camera straight at the light & shot it at my fastest exposure, 1/4000s The result is a bit blurry, because a) there's a diffuser on it & b) it was too squinty to really want to gaze at more than necessary.
However, the salient point is that even at 1/4000 I cannot find any dark LEDs or sign that they are flickering at all, even with multiple shots.
This picture with the light intensity set to minimum, but I saw the same results at various brightnesses, no hint of flicker or 'scanning'.
Have we reached the point where we can have fully dimmable [& had I paid extra, temperature variable] LED panels, without any flicker, or at least flicker that can't be seen at 1/4000s?
Or is there error in my method?
Histogram from the picture