You are underway and pass by a lighthouse. Its light, which was white since you first sighted it, changes to red. This means __________.

Correct Answer: Option C — you have entered an area of shoal water or other hazard

Sector lights are designed to provide directional guidance. A change in color, such as white to red, indicates that the vessel has moved out of the safe white sector and into a danger sector, typically signifying the presence of shoal water or other navigational hazards nearby.