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Filmmaking Dictionary: Number 6 / 60 Hz Mains Frequency
Definition
60 Hz mains frequency means an alternating-current electrical supply completes sixty cycles per second. It is the nominal mains frequency in Canada and the United States, among other places. Frequency and voltage are separate electrical specifications.
On a film set, 60 Hz often matters because certain light sources vary in brightness in relation to the supply. The camera can reveal that variation as flicker or bands. Modern drivers, dimming methods and displays may operate at other frequencies, so mains frequency is only part of the explanation.
Camera Timing and Light Output
Some sources produce light variation at twice the mains frequency, or about 120 cycles per second on a 60 Hz supply. Other sources have different modulation patterns. Exposure duration and sensor readout determine how the camera samples that changing output.
A light that appears steady during a walkthrough may fail a high-frame-rate test. Changing dimmer level can also change its behaviour. Test the actual fixture, output level, camera mode and shutter setting used for the shot.
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Useful Timing Examples
- At 30 fps, a 180-degree shutter corresponds to approximately 1/60 second.
- At 60 fps, a 180-degree shutter corresponds to approximately 1/120 second.
- At 24 fps, a 144-degree shutter corresponds to approximately 1/60 second.
- These relationships can guide a test, but they do not guarantee a clean image from every source.
Example on Set
A 24 fps scene includes existing commercial ceiling lights. The crew sees brightness changes at the usual 180-degree shutter. Testing a shorter 144-degree angle may help with a source linked to 60 Hz timing, but the change also reduces exposure and motion blur.
If the flicker remains, the fixture’s driver or the camera’s readout may be responsible. Replacing or switching off the problem source, changing its operating mode or revising the lighting plan can be more reliable than choosing increasingly unusual shutter settings.
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Frequently Asked Questions
Does a 60 Hz location require shooting at 60 fps?
No. Capture and delivery rates are chosen separately. Lighting must be tested for the chosen camera settings.
Does a 60 Hz label prove that a fixture works on any North American supply?
No. Voltage, current, connectors and the manufacturer’s permitted input range still matter. Frequency alone does not establish compatibility.
Related Terms
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