Why camera images have diagonal flicker bands

You may see slanted dark or bright stripes in a webcam preview, a phone photo, or a video recorded indoors. They can appear only under certain lights, change as you move the camera, or vanish when you take the camera outside.

The pattern often comes from a mismatch between changing light and the way a camera reads an image. A quick comparison with the Camera Test can help you separate a lighting issue from a camera or browser problem.

Check when the bands appear

1. Open the Camera Test and allow camera access when your browser asks.
2. Point the camera at a plain, stationary area under the light where you noticed the bands. Watch the live preview for a few seconds.
3. Keep the camera in place and switch off that light, or move into daylight. Compare the preview without changing anything else.
4. Turn the light back on, then move the camera slightly or point it at a different part of the room. Notice whether the bands change position, angle, or spacing.
5. If possible, check the same scene in another camera app or browser. Compare the preview, reported resolution, and frame rate.

Change just one thing at a time. That makes it easier to tell whether the pattern follows the light, the camera, or the software displaying the image.

What the result means

The bands disappear when you switch off a lamp

The light is the likely cause. Many LEDs do not produce perfectly steady light. Their brightness can pulse rapidly because of the power supply or a dimming method called pulse-width modulation. Your eyes may not notice the pulses, but a camera can capture them.

The bands remain in daylight and in different apps

The cause may be a camera setting, a connection problem, or the camera hardware. If this is a USB webcam, reconnect it and test another port. If the same pattern appears in every app and under several kinds of light, look for exposure or anti-flicker controls in the camera's own software.

The pattern changes when you move the camera

This can still be light flicker. A camera often reads the image one row at a time rather than capturing every row at the same instant. This is called a rolling shutter. As the light changes during that scan, different rows can record different brightness levels. Panning or rotating the camera can make the bands appear to shift or tilt.

The lines follow fine details, not the lighting

The pattern may be moiré instead of flicker. Moiré is a false pattern created when small repeating details, such as fabric weave or a screen grid, interact with the camera sensor. Change the distance or angle, or focus on a different area. Moiré usually follows the detail in the scene; flicker bands often change when you change the light or exposure.

The bands appear only when filming a monitor or TV

The camera may be capturing the screen as it refreshes. The display updates in cycles, and the camera reads its image at a different rate. Try changing the camera angle, frame rate, or shutter setting if those controls are available. A screen recording is a better choice when you need to capture what is displayed on a computer.

How to reduce the bands

1. Use steadier lighting. Try daylight or a different lamp. If the bands stop under the new light, replace or avoid the lamp that triggers them. Dimming an LED can make flicker worse, so test it at full brightness too.
2. Turn off automatic dimming on the light. Test the lamp without a dimmer, smart lighting effect, or low-brightness setting. Some LED bulbs flicker even when they are not dimmed, so a different bulb may be needed.
3. Choose an anti-flicker setting. If your camera software offers Anti-flicker or Anti-banding, try the setting that matches your region's electrical frequency, usually 50 Hz or 60 Hz. This option is not available on every webcam or phone.
4. Adjust exposure if you can. In a camera app with manual controls, try an exposure time that matches the local lighting cycle, such as 1/50 or 1/60 second. For video, use a frame rate and shutter setting that work with the light. Webcam apps often hide these controls, so the camera test itself may not be able to change them.
5. Check camera access and reconnect the device. On Windows 11, open Settings › Privacy & security › Camera. On macOS, open System Settings › Privacy & Security › Camera. Check that the browser or camera app is allowed, then reconnect a USB camera or restart the phone if the image remains abnormal.
6. Compare another camera app or browser. If the bands appear in only one app, check that app's video settings and update it. If the same defect follows the camera across apps, lighting, and devices, investigate the camera or its driver instead.

On a phone, also try the built-in camera app's anti-flicker or anti-banding option if it has one. Menu names differ by model. When testing a phone camera in a browser, allow camera permission for the browser in the phone's privacy settings.

Why diagonal bands can appear

A rolling shutter does not expose the whole sensor at once. It reads rows in sequence, while the light may brighten and dim many times during that process. The camera can therefore record one part of the image at a brighter moment than another. The exact shape and direction depend on the camera's sensor readout, the light source, exposure, and camera movement. Diagonal bands alone do not prove that the sensor is damaged.

The Camera Test can show whether a camera preview works and report its resolution and frame rate, but a browser cannot directly identify a lamp's flicker frequency or provide every camera's manual exposure controls. A clean preview under steady light is a useful sign that the bands are caused by the lighting and capture timing, not a permanent image defect.

The Camera Test asks for permission before using the camera, and the live preview stays on your device.