Under what condition must vessels have navigation lights during restricted visibility?

Vessels must have navigation lights during periods of restricted visibility to ensure safety on the water. Restricted visibility can occur due to various conditions such as fog, rain, snow, or darkness, where a vessel's ability to see and be seen is significantly impaired. The lights serve as a critical communication tool between vessels, allowing them to determine the presence and position of other boats, which helps prevent collisions and enhances overall navigational safety.

Using navigation lights is mandatory regardless of the vessel's length or the specific weather conditions, making it essential to adhere to these regulations every time visibility is restricted. The requirement is not limited to foggy conditions alone; it also applies in any situation where visibility is diminished. Therefore, the obligation to use lights extends to all vessels when navigating under such conditions, reinforcing safe boating practices.