What does it mean when you observe a red and a green light but no white light?

Observing a red and a green light but no white light indicates that you are likely approaching a sailing vessel that is under way. In maritime navigation, vessels display specific lighting to indicate their type and status.

For powered vessels, typically, you would see a white light combined with the side lights (red and green) when they are underway at night. In the case of a sailing vessel, if it is under sail, it will show the red light on the port (left) side and the green light on the starboard (right) side. The absence of a white light suggests that the vessel is not a power-driven craft or does not have its anchor lights displayed, which is consistent with the configuration of a sailing vessel under sail.

In busy waterways, the presence of red and green lights without white also rules out a congested area, as congested areas may present additional navigational markers or lights. The same logic applies to stationary objects, as those would likely have a white light for visibility. Thus, recognizing this lighting pattern is essential for safe navigation and situational awareness on the water, clarifying that you should be alert for a sailing vessel ahead.