Flicker-Free Shutter Calculator

Knowledge Base

Why Shutter Speed Causes Flicker

Mains-powered lights that aren't on a flicker-free driver actually pulse at twice the mains frequency. A 60Hz supply produces 120 pulses per second, and a 50Hz supply produces 100. If your shutter is open for a duration that isn't a whole multiple of that pulse period, you capture a different amount of light in each frame, which shows up as visible banding or flicker, especially in slow motion or when panning past fluorescent tubes.

The Rule of Thumb

Match your region's mains frequency to your shutter speed family: on 60Hz power, shutter speeds like 1/60, 1/120, and 1/240 are safe. On 50Hz power, use 1/50, 1/100, or 1/200. This is why many cameras default to a 180-degree shutter at a frame rate matching local power. It lines up automatically.

What About LED Lights?

Cheap LED panels and practicals often flicker at mains frequency just like old fluorescent tubes, so the same safe shutter speeds apply. Higher-end LED fixtures with flicker-free or high-frequency drivers (and continuous sources like daylight, tungsten, or HMI on a flicker-free ballast) don't pulse at all, so any shutter speed is safe from a flicker standpoint, though the 180-degree rule still applies for natural motion blur.

FAQ

Q: I'm shooting slow motion at a high frame rate, does the rule change?
A: No, the safe shutter speeds are still whole multiples of the mains pulse period, but at high frame rates you may need a much faster shutter than a 180-degree angle would give you, which can mean stepping outside 180 degrees or accepting some risk of flicker.

Q: My mains frequency is right but I still see flicker, why?
A: Some ballasts and drivers (particularly older or faulty ones) don't produce a clean, symmetric pulse: try the next safe shutter speed up or down, or test in-camera before the real shoot.

Worked examples: safe shutter speeds by mains frequency

Shutter speeds that avoid banding under mains-powered lighting, for both mains standards and the frame rates most work uses. Lights on alternating current pulse twice per cycle, so a 50 Hz supply flickers 100 times a second.

A safe shutter speed is one where the exposure covers a whole number of light pulses, so every frame receives the same amount of light. Where the 180 degree shutter and the nearest flicker-free speed differ, you are choosing between natural motion blur and clean exposure. Under LED or tungsten light run without dimmers, neither constraint applies.

Vocabulary

Mains frequency. How many times per second the alternating current supply reverses, 50 Hz across most of the world and 60 Hz in North America. Lighting pulses at twice this rate, because a bulb brightens on both halves of each cycle.

Banding. Horizontal light and dark bars rolling through footage, caused by the sensor reading different rows while the light output is changing. Not fixable in post in any reliable way, so it has to be avoided at the shutter.

Shutter angle. A way of expressing shutter speed relative to frame rate, inherited from rotating film shutters. A 180 degree shutter exposes for half of each frame, which at 24 fps means 1/48 second and produces the motion blur audiences read as cinematic.

Flicker-free lighting. Fixtures with electronics smoothing their output, so brightness stays constant instead of pulsing with the supply. With these you pick shutter speed for motion blur alone.