When is the all-around white light used as an anchor light?

The all-around white light is used as an anchor light when sidelights are extinguished because it serves to indicate the vessel's presence to other boaters while at anchor. This light provides visibility and helps prevent collisions by allowing other vessels to see that the anchored boat is not underway and its position is marked.

In situations where a vessel is not moving, typically, it should display an all-around white light to signify that it is at anchor. This helps maintain safety, especially in crowded or poorly lit waters. The other options do not accurately describe scenarios where the all-around white light specifically serves its purpose as an anchor light.