Weird PWM effect on digital camera

[Fallingwater]

I just took a picture of a cheapo 3AAA flashlight which I modified with a 2-mode buck driver and a 18650 cell. It was running in low mode, so PWM was active. The picture came just fine, but the display of the camera showed this:

(the crack is not in the screen, but on the plastic protection I glued on it)

Sorta looks like a tiny piece of the matrix
I just found it curious and thought I'd share the pic.

 

[Search]

It's not your camera man. It's a beacon..

run

 

[balou]

A digital image sensor is basically just a huge bank of capacitors. At first they get charged, then the shutter opens, and the brightness level at that pixel is determined by how much the capacitor is discharged. The light is too bright for your camera to handle, so the light not just discharges one little capacitor a.k.a. pixel, but a whole row. The pixels should be isolated from each other, but only up to a certain point.

While shooting, the shutter gets closed, caps charged up, and then the shutter is opened for a short time. You see the rows of light.
But on live view, the caps have to be charged continously (which degrades image quality, that's why there's still a shutter on any camera capable of taking acceptable pictures). So now the cap recharge fights against the continous discharge caused by the bright light.
Or not continous, as its PWM. In that case, it's most likely that while the light is on, everything gets discharged equally, but the cap recharge of the camera has to little time to recharge all the pixels until PWM kicks in again, so some of them remain dimmer.

I guess the dots are moving? Would be quite a coincident else, that would mean that the frequency of the PWM and the sensor update frequency are multiplies of eachother