Flicker Checker

Why Does Flicker Happen?

Most artificial light sources — fluorescent tubes, LED panels, HMI lights — are powered by AC electricity and therefore pulse at twice the mains frequency: 100 times per second in Europe (50 Hz grid) and 120 times per second in the USA (60 Hz grid). To the naked eye this is invisible, but a camera can expose a frame during a darker pulse, a brighter pulse, or anything in between — which shows up as flickering banding or brightness variation in the footage.

If each frame's exposure time is an exact multiple of the light cycle, the camera always captures the same average brightness — no flicker. For a 50 Hz grid (light cycle = 1/100 s), the safe shutter speeds are 1/25, 1/50, 1/100. For a 60 Hz grid (cycle = 1/120 s): 1/30, 1/60, 1/120.

The shutter time can never exceed one full frame (360°). So as FPS rises, slower safe shutters drop out. At 72 fps with a 50 Hz grid, 1/25 and 1/50 would both require angles above 360° — only 1/100 remains valid. At 120 fps the frame time (1/120 s ≈ 8.3 ms) is shorter than even 1/100 s (10 ms), so no standard flicker-free shutter is possible — consider a continuous, flicker-free light source instead.