What light combination indicates a vessel that is aground at night?

The indication of a vessel that is aground at night is best represented by two red lights displayed in a vertical line. This combination is part of the International Regulations for Preventing Collisions at Sea (COLREGs), specifically outlining specific light signals for different scenarios.

When a vessel is aground, it needs to signal its situation to ensure safety and avoid collisions. The two red lights vertically aligned are universally recognized as the signal for a vessel that has run aground. This signal alerts other nearby vessels that they should exercise caution and avoid the area, as it indicates a potential hazard.

The other light combinations do not convey the same message of being aground. For instance, a white all-around mast light would typically indicate that a vessel is at anchor or may be a part of other navigation signals but does not specifically indicate grounding. Similarly, three red lights in a triangular formation and anchor lights with a green light are not recognized signals for a grounded vessel. Such signals are associated with different circumstances and do not convey the urgency or warning required for a vessel aground.