Guide
How to prevent flicker when filming on iPhone
Flicker can be fixed afterwards, but it's always better not to record it in the first place. Most of it comes down to three things: the light you film under, the frame rate you pick, and, if you can control it, the shutter speed. Here's what actually works on an iPhone, including what the built-in Camera app can and can't do.
Know your mains frequency
Everything below depends on whether your power runs at 50 Hz or 60 Hz, because lights on that supply pulse at twice that rate. If you're not sure, a quick search for your country's mains frequency will tell you.
| Mains power | Where (examples) | Lights pulse | Flicker-safe shutter speeds |
|---|---|---|---|
| 60 Hz | US, Canada, Mexico, South Korea, Taiwan | 120 times a second | 1/60 s or 1/120 s |
| 50 Hz | UK, Europe, Australia, most of Africa and Asia | 100 times a second | 1/50 s or 1/100 s |
Japan is split: 50 Hz in the east, 60 Hz in the west. For the physics behind this, see why slow-motion video flickers.
1. Film under light that doesn't flicker
The surest fix is a steady light source.
- Daylight doesn't flicker. Moving your subject near a window, or outdoors, solves the problem completely.
- Video lights sold for filming often advertise flicker-free operation. If you buy one, test it at the frame rate you plan to use, at the brightness you plan to use.
- Swap or switch off the worst fixture. One cheap LED bulb or an old fluorescent tube can be the whole problem. If you control the room, turning off a single light sometimes cleans up the shot.
2. Only shoot slow motion when you need it
At normal frame rates the camera can expose each frame long enough to average out the light's pulses. At 120 and 240 fps it can't. If you don't actually need slow motion, film at 24, 25 or 30 fps (Settings › Camera › Record Video) and most flicker simply doesn't appear.
In 50 Hz countries, turning on Show PAL Formats in the same Record Video menu adds 25 fps options. That frame rate divides evenly into 100 Hz light, which helps the camera avoid flicker.
When you do want slow motion, choose the frame rate that suits your power supply (Settings › Camera › Record Slo-mo):
- 60 Hz countries: prefer 120 fps over 240 fps. At 120 fps each frame lines up with one 120 Hz light pulse, so the brightness stays much steadier. At 240 fps you get two frames per pulse and they can alternate bright and dark.
- 50 Hz countries: neither 120 nor 240 fps divides into 100 Hz, so slow motion under mains-powered light will usually show some flicker. Daylight or flicker-free lights matter more here.
3. Match the shutter speed to the mains (manual app needed)
The built-in Camera app doesn't let you set the shutter speed for video. It chooses the exposure automatically. To control it you need a manual camera app such as Blackmagic Camera, which lets you set the shutter speed or shutter angle yourself.
Set the shutter to a whole number of light pulses: 1/60 or 1/120 s on 60 Hz power, 1/50 or 1/100 s on 50 Hz power. Every frame then collects the same amount of light, wherever the pulses fall, and both flicker and bands disappear. Control brightness with ISO instead of shutter speed.
If the app uses shutter angle rather than speed, the angle that matches depends on the frame rate. The formula is angle = 360 × frame rate × exposure time:
- 30 fps on 60 Hz power: 180° gives 1/60 s.
- 25 fps on 50 Hz power: 180° gives 1/50 s.
- 24 fps on 60 Hz power: 144° gives 1/60 s.
- 24 fps on 50 Hz power: 172.8° gives 1/50 s.
There's one hard limit. The exposure can't be longer than the time between frames. At 120 fps the only flicker-safe option is 1/120 s, a full 360° shutter on 60 Hz power, if your app allows it. At 240 fps no exposure is long enough to cover a whole light pulse, so shutter matching can't help and the other steps in this guide matter more.
4. Lock the exposure
In the Camera app, touch and hold on your subject until AE/AF LOCK appears, then drag the sun icon up or down to adjust brightness. Locking stops the camera from constantly re-adjusting exposure as the light pulses and as people move through the frame.
Exposure lock doesn't remove flicker by itself. It does stop the extra brightness pumping that auto-exposure adds on top, and that makes whatever flicker remains much easier to correct afterwards. In a manual app, setting ISO and shutter by hand does the same job.
5. Avoid dimmed LEDs
Many LED dimmers work by switching the light on and off very rapidly (pulse-width modulation). The lower the setting, the longer the off periods, and the harsher the bands in slow motion. If you can, run LED lights at full brightness and control the level by moving the light or using fewer fixtures. The same applies to the brightness setting of LED strips and smart bulbs, and to screens in the shot, many of which dim their backlight the same way.
6. Test before the moment that matters
Flicker is easy to miss on a small screen until you play the clip back slowed down. Before the real take:
- Switch to Slo-mo and watch the viewfinder for bands.
- Record a few seconds of the scene.
- Play it back in Photos and look at walls, ceilings and skin tones, where flicker shows up most clearly.
- If it flickers, change one thing (frame rate, a light, your position) and test again.
Two minutes of testing beats discovering the problem after a once-only moment.
If flicker gets in anyway
Sometimes there's no choice: the venue's lights are what they are and the moment won't repeat. That's fine. Flicker in footage you've already shot can usually be corrected. See how to fix flickering slow-motion video on iPhone, and for LED-heavy venues, how to remove LED and fluorescent flicker.
