When the camera's night-vision infrared (IR) is active (in low-light or nighttime situations), the IR LED can reflect off obstructions and back into the camera. This can cause a white ring effect in the video feed.
If you can, adjust the camera angle and position so the camera's field of view ("IR LED Coverage" in the diagrams below) is clear of obstructions.
See the diagrams below for examples of correct installation.