PWM and banding

[cuxlander]

Hello,
I am using a makeshift LED with PWM dimming. Frequently I experienced strong banding.
Then I forgot to remove a POL-foil from the in-base illuminator. No more banding.
Does this make sense?
Cheers,
Hans

[MichaelG.]

Mmm ... only if it significantly changed the exposure time on your camera, or meant that the LED was on for longer.

The banding is essentially a ‘beat frequency’ problem, but changing the mark/space ratio of the PWM can mask it.

MichaelG.

[daruosha]

Do you know the base frequency of the PWM driver and its minimum duty cycle? That would explain the mystery a bit.

[MicroBob]

Hi Hans,
the polarizer reduced brightness quite a bit and you will have turned up the power source of LED. The PWM dimming just takes place whet less than full power is used - the lower the brightness the longer the gaps. For photography you might just use an ND filter that allows photography at fully power.

Bob