PWM (pulse-width modulation) is a method of controlling LED output by changing how long the LEDs are driven on within repeating switching cycles. The on-time proportion is the duty cycle; the number of cycles per second is the PWM frequency.
Why cameras can see it
A light may look steady to the eye while a camera records variation between frames or bands across the image. The result depends on modulation, exposure time, sensor readout and dimming level. A higher frequency can reduce problems, but a single frequency figure is not a universal flicker guarantee.
Dimming and control are separate
A DMX dimmer value is a command sent to the fixture. PWM is one way the fixture’s electronics can produce the requested output. DMX refresh rate and LED switching frequency are different quantities.
Practical example
Test an LED at the low dimming level and fast shutter required for a shot. If bands appear, check whether the fixture offers frequency selection or a high-speed mode, and test the changed setting on the actual camera. Also check whether the mode limits output, dimming or colour control.
Related terms
Flicker · DMX512 · Watt · Dimming Curve
References
ENTTEC: PWM and camera shutter timing · Aputure: LS 600d frequency selection