How to stop webcam flicker on a Mac

01Why it happens

Most indoor lights don't shine steadily. Fluorescent tubes and many LED bulbs run on alternating current, and they brighten and dim twice for every cycle of it. On 50 Hz power that is 100 pulses a second. On 60 Hz power it is 120. Your eyes average that out. A camera doesn't.

Most webcams read the picture one row at a time. If the exposure doesn't cover a whole number of light pulses, some rows catch more light than others. You see dark bands rolling up or down the frame, or the whole picture pulsing.

Rolling dark bands under LED or fluorescent light almost always mean anti-flicker is set wrong.

0250 Hz or 60 Hz?

Most USB webcams have an anti-flicker control. The USB camera standard calls it power line frequency. It tells the camera the rhythm of your lights so its auto exposure can stay in step. It has to match the power where you are, not where the camera was sold.

• 60 Hz: the United States, Canada, Mexico, Brazil, Colombia, South Korea, Taiwan, the Philippines, Saudi Arabia, and western Japan.
• 50 Hz: the UK and most of Europe, most of Africa, Australia, New Zealand, China, India, and eastern Japan, including Tokyo.
• Not sure? Look up your country's mains frequency, or try both settings and keep the one where the bands go away.

Some cameras also offer Off and Auto. Auto lets the camera work out the frequency itself. Off is for daylight, or for lights that don't flicker.

03What macOS gives you

Not much, honestly. macOS has no anti-flicker setting for USB webcams, and no exposure controls either. The video effects in the menu bar's Video menu, like Portrait, Studio Light, and background replacement, change how the picture looks. None of them change the camera's timing, so none of them remove banding.

Without an app that can reach the control, the camera keeps whatever setting it already has, in every app you use it with.

04Other things that help

• Use daylight. It doesn't flicker. Facing a window, or opening the blinds, can be enough on its own.
• Turn dimmers all the way up, or switch dimmed lights off. Many LEDs dim by switching on and off hundreds or thousands of times a second, and no anti-flicker setting matches that.
• Find the culprit. If the bands only appear when one lamp is on, that lamp is the one to change.
• Swap the bulb. A cheap LED bulb or a tired fluorescent tube is often the whole problem. Bulbs sold as flicker-free are worth trying.

05Fix it with Webcam Works

1. Open ImageSelect your USB webcam, then choose Image in the sidebar under Source.
2. Set Anti-flickerSet Anti-flicker to your country's power line frequency: 60 Hz in the US, 50 Hz in most of Europe. The row only shows the options your camera accepts, so you may also see Off or Auto.
3. Check the previewThe change goes to the camera straight away. If the bands stop, you're done. If they get worse, try the other frequency.
4. Match exposure time if you set it by handOn many cameras, anti-flicker only guides the camera's own auto exposure. If Auto exposure on the Exposure card is Off, the Exposure time you pick decides. On 50 Hz power, aim for 10 or 20 ms. On 60 Hz power, aim for 8.3 or 16.7 ms.
5. Save itIn Presets, choose New from current. Anti-flicker is saved with the rest of the camera's settings.

06Tips

• Those exposure times are 1/100 and 1/50 of a second for 50 Hz, and 1/120 and 1/60 for 60 Hz. The Exposure time row shows milliseconds. Some cameras only accept certain steps, so get as close as the slider allows and watch the preview.
• Smart AE picks exposure times itself and doesn't line them up with your lights. If bands show up while it's on, switch Auto exposure to Camera AE, or to Off and set the time by hand.
• The built-in presets set Anti-flicker back to the camera's own default. If flicker returns after you apply one, set it again and save your own preset.
• Slow brightening and dimming is a different problem. That is usually auto exposure reacting to the room, and taking exposure manual stops it.
• Built-in Mac cameras and iPhone Continuity Camera don't offer this control. It is for USB webcams.
• After the 14-day trial, the Exposure card stays free, so matching exposure time by hand keeps working. Anti-flicker is on the Image card, which is part of the $9.99 one-time unlock.