Last Updated 39 minutes ago
Filmmaking Dictionary: Number 5 / 50 Hz Mains Frequency
Definition
50 Hz mains frequency means an alternating-current electrical supply completes fifty cycles each second. It is common in many countries. Frequency is a different specification from voltage: knowing that a supply is 50 Hz does not tell you its voltage, available power or connector requirements.
For filmmakers, the term often comes up when matching camera timing to practical lights, discharge sources, LED fixtures or displays. The electrical supply can affect light output, but the visible modulation also depends on the equipment’s internal electronics.
Why Flicker Appears
Some mains-driven lights fluctuate at twice the supply frequency, while other fixtures use drivers or dimming systems with quite different behaviour. A camera can record changing brightness or moving bands when its exposure timing interacts with that variation.
A fixture that looks steady to the eye may still cause problems on camera. High frame rates, short shutter times and certain dimming levels can reveal modulation that was hidden during a normal-speed test. Rolling sensor readout can also turn timing differences into bands.
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Common Timing Relationships
- At 25 fps, a 180-degree shutter gives approximately 1/50 second.
- At 50 fps, a 180-degree shutter gives approximately 1/100 second.
- At 24 fps, a 172.8-degree shutter gives approximately 1/50 second.
- These are useful starting relationships, not guarantees for every fixture or screen.
Example on Location
A crew shooting 24 fps in a room with existing ceiling lights notices flicker at 1/48 second. Testing 1/50 second may help with a source tied to a 50 Hz supply. If the problem remains, the driver, dimming setting or camera readout may require another approach.
The test should include the actual fixture intensity, colour mode and shooting speed. Replacing a problematic practical, using a suitable film fixture or adjusting the scene may be more reliable than trying to rescue severe flicker in post.
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Frequently Asked Questions
Does 50 Hz power require a 25 fps film?
No. Frame rate is a creative and delivery choice. Lighting and exposure timing need to be managed for that choice.
Can equipment marked only for 60 Hz be assumed compatible?
No. Check its specified input range and power requirements. Camera timing advice does not establish electrical compatibility.
Related Terms
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