Refresh rate and camera

What is refresh rate?

The refresh rate is the number of times per second the LEDs of the screen are driven again, in hertz (Hz). That is not the same as the frame rate of your video, which is 25, 50 or 60 frames per second.

An LED screen refreshes each video frame many times. At 3,840 Hz and 60 frames per second that is 64 times per frame.

Why does a camera see what you do not?

LEDs dim by switching on and off very quickly. Your eye averages that out. A camera with a short shutter time captures only a fraction of a second. If that exposure falls badly between refreshes, you see dark bands, flicker or rolling lines in the picture. The higher the refresh rate, the smaller that chance.

Which value do you need?

• 1,920 Hz: common for fixed screens that are mostly viewed by eye, such as advertising and information.
• 3,840 Hz: common for rental and stage, where cameras and phones are watching.
• 7,680 Hz: for demanding camera work, such as broadcast, short shutter times and virtual production.

These are guide values. The result also depends on the shutter time, on the brightness the screen runs at and on the processor.

More than hertz alone

A screen that runs heavily dimmed has a harder time: at low brightness, refresh and greyscale drop on many screens. So test at the brightness you use during the show. For broadcast you synchronise the camera and the screen processor with genlock.

Moiré, the wave pattern you sometimes see on camera, has a different cause: the grid of the pixels clashes with the grid of the camera sensor. You solve that with distance, focus or a finer pitch, not with a higher refresh rate.

How to test it

Film the screen beforehand with the camera and the shutter time of the production. Run the screen at show brightness. If you see no bands during a slow pan, you are fine.

Examples from the catalogue

The values below come straight from the catalogue.