Refresh rate and scan rate are often quoted interchangeably, but they describe different parts of the driving chain. Refresh rate (measured in Hz) is how many frames the receiving card outputs to the module per second. Scan rate (1/N scan, e.g. 1/16, 1/32) is how many LED rows are lit simultaneously per driver IC cycle - most common panels are not lit all at once, but row by row, relying on persistence of vision.
This distinction matters because problems blamed on "low refresh rate" (visible bands on camera, flicker) are frequently caused by the scan duty cycle, PWM modulation of the driver IC, and phase alignment between row scans, not by the frame rate alone.
How PWM scanning creates camera flicker
Driver ICs modulate brightness with PWM at a certain frequency. When a camera shoots the screen, its shutter samples this modulation at a different rate, producing rolling bands or flashing frames. Three factors determine how visible this is:
- PWM frequency - higher frequency shifts band patterns beyond what typical shutter speeds capture, but raises switching losses.
- Blanking and phase alignment - receiving cards that align PWM phases across cabinets reduce low-frequency beats that appear as slow-moving bands on camera.
- Shutter speed interaction - the same screen can film cleanly at 1/100s and terribly at 1/50s, which is why on-site verification matters more than a spec-sheet number.
What refresh rate different applications need
- Broadcast studios and XR/virtual production: 3840 Hz above is the practical baseline; genlock (frame sync to camera) and low-latency processing matter as much as raw refresh rate. To avoid overlap with existing moiré article: here the issue is temporal (flicker, sync), there it was spatial (patterns from pixel grid and lens).
- Indoor rental for conferences: 3840 Hz is commonly specified since phones film constantly; phase alignment between receiving cards avoids cabinet-to-cabinet banding.
- Fixed outdoor/traffic signage: cameras usually view from a distance at higher shutter speeds; 1920–3840 Hz usually suffices, and driving efficiency may weigh more than extreme refresh numbers.
How to verify before accepting a spec
A numeric claim like "refresh rate 7680 Hz" is only meaningful with context. Practical checks:
Film the panel with a phone at several shutter speeds and look for banding.
Check uniformity across cabinets - banding that moves between cabinets indicates phase misalignment, not low refresh rate.
Test at low brightness, since PWM duty narrows at low grey levels and flicker worsens there.
Takeaway
Refresh rate is a headline number, but flicker control is a system property: driver IC PWM frequency, receiving-card phase alignment, scan scheme and brightness level all interact. Matching the driving scheme to the actual filming environment - rather than chasing the largest number - gets predictable on-camera results.