Which light is specifically defined as showing an unbroken light over an arc of the horizon of 225 degrees?

The masthead light is specifically defined in the COLREGs as showing an unbroken light over an arc of the horizon of 225 degrees. This type of light is displayed on vessels that are underway, and it helps to indicate the presence and heading of the vessel to other nearby vessels.

According to the COLREGs, the masthead light is usually positioned at the highest point of the vessel to maximize its visibility, ensuring that it can be seen by other vessels from a significant distance, particularly from the front and the sides. The specification of 225 degrees means that the light should be visible from the bow and for a substantial portion of the sides, which is crucial for collision avoidance at night or during periods of reduced visibility.

In contrast, other types of lights serve different purposes and have different visibility arcs. For instance, side lights cover 112.5 degrees each and are used to show the port and starboard sides of a vessel, while a stern light covers 135 degrees and is displayed from the back of the vessel. A towing light typically has a different specification as well, as it indicates that the vessel is engaged in towing operations but does not have the same configuration as the masthead light.