When must navigation lights be on for power-driven vessels?

Navigation lights for power-driven vessels must be activated during periods of restricted visibility. This is critical for safety reasons, as diminished visibility can be caused by factors such as fog, rain, or darkness. The use of navigation lights in these conditions helps ensure that a vessel is visible to other boats and allows for safer navigation in shared waterways.

While navigation lights are also required at night, they are specifically mandated during any time when visibility is compromised, which encompasses more scenarios than just nighttime. This broad definition of restricted visibility includes a variety of circumstances where visibility may be limited, thus necessitating the use of navigation lights to avoid collisions and enhance safety on the water.