Video & LED calculator
LED Wall Camera Shutter / Flicker Calculator
LED walls dim by pulsing their LEDs (PWM) at the panel refresh rate, and a camera shutter that captures less than one full refresh cycle catches unequal light between rows of the scan, which reads as rolling bands. Enter the wall refresh rate and your shutter to see how many cycles each exposure captures.
From the panel/processor spec: 1920 Hz on budget walls, 3840 Hz and up on broadcast-grade.
Formulas
Exposure time
t = 1/shutter, or t = (angle / 360) / fps- shutter:
- shutter speed denominator, e.g. 250 for 1/250 s
- angle:
- shutter angle in degrees for cinema cameras
Cycles captured
cycles = refresh(Hz) × t(s)- refresh:
- LED panel refresh rate in Hz
How it works
A rolling-shutter camera exposes the sensor line by line. If the exposure window covers at least one complete PWM refresh cycle, every line integrates the same amount of wall light and the image is clean. When the window is shorter than a cycle, different lines catch different slices of the pulse train and the wall breaks into bright and dark bands that crawl with any clock drift.
The arithmetic is forgiving with fast walls: at 3840 Hz refresh, one cycle lasts 0.26 ms, so even a 1/2000 s shutter (0.5 ms) captures nearly two full cycles. At 1920 Hz the margin halves, and low-refresh signage panels (below 1000 Hz) band under almost any broadcast shutter. That is the whole reason broadcast and virtual-production walls advertise 3840 Hz and beyond.
Frame rate matters only through the shutter: 60 fps at a 180° shutter is an 8.3 ms exposure, which is safe on nearly anything, while high-speed or short-shutter work is where walls fail. Genlocking the wall processor to the camera system and adjusting processor phase can clean up marginal cases; multiplexed "scan" ratios on cheap panels can still beat you regardless.
Worked example: Broadcast camera at 1/250 s on a 3840 Hz wall vs a 960 Hz signage panel
- 1.Exposure: 1/250 s = 4 ms.
- 2.On 3840 Hz: 3840 × 0.004 = 15.4 cycles captured. Clean.
- 3.On 960 Hz: 960 × 0.004 = 3.8 cycles: still fine. At 1/2000 s (0.5 ms) the same panel captures 0.48 cycles and bands.
The shutter, not the frame rate, decides; short shutters need high-refresh walls.
Cycles captured at common shutters
| Shutter | Exposure | 960 Hz wall | 1920 Hz wall | 3840 Hz wall |
|---|---|---|---|---|
| 1/60 s | 16.7 ms | 16.0 | 32.0 | 64.0 |
| 1/250 s | 4.0 ms | 3.8 | 7.7 | 15.4 |
| 1/1000 s | 1.0 ms | 0.96 | 1.9 | 3.8 |
| 1/2000 s | 0.5 ms | 0.48 | 0.96 | 1.9 |
| 1/4000 s | 0.25 ms | 0.24 | 0.48 | 0.96 |
Field notes
- Test with the actual show camera and shutter at the actual wall brightness; refresh behavior on some processors changes with brightness and bit depth.
- Moire is the other camera-versus-wall failure and has nothing to do with refresh; it is pixel pitch against sensor resolution, fixed with focus, distance, or slight defocus.
Frequently asked questions
What shutter speed stops LED wall flicker?
Any shutter whose exposure covers at least one full refresh cycle, ideally two or more. Divide the refresh rate into 1: a 1920 Hz wall wants exposures no shorter than about 1/1000 s for margin.
What LED refresh rate do I need for filming?
Broadcast and on-camera walls typically spec 3840 Hz or higher, which stays clean down to very short shutters. 1920 Hz survives normal broadcast shutters; low-refresh signage panels are the ones that band.
Why does the wall look fine to the eye but band on camera?
Eyes integrate over tens of milliseconds and cannot resolve kilohertz PWM. Cameras with millisecond and sub-millisecond exposure windows sample the pulse train and expose the modulation.