This is a rolling-shutter effect. Phone cameras usually don’t expose the whole sensor at exactly the same instant; they scan the image line by line. A lightning flash is extremely brief, so only part of the sensor is being read when the scene suddenly gets much brighter. That creates a bright vertical band in the final photo.

It’s more noticeable on phones because their sensor readout is often slower than on higher-end cameras. A similar effect can happen under flickering fluorescent lights.

How to avoid it:

• You usually can’t eliminate it completely on a phone.
• A camera with a faster readout or a true global shutter would reduce it.
• Since lightning is unpredictable, timing/exposure tricks are limited.

How to fix it afterward:

• There’s no simple automatic correction, because part of the frame genuinely received different exposure.
• Basic editing apps may let you reduce the band with local adjustments or gradients, but results will vary.
• If the band is severe, the best solution is often to keep another frame instead.