group-flashing light

A group-flashing light is a type of signal used by lighthouses to help mariners navigate. These lights are characterized by a specific pattern of flashes and eclipses that repeat at regular intervals, serving as an identification signal.1

Lighthouses use various patterns to distinguish themselves. A group-flashing light typically exhibits groups of two, three, or four flashes. A short eclipse occurs between individual flashes within a group, followed by a longer eclipse of several seconds between successive groups. This entire pattern then repeats at set intervals, such as every 10 or 20 seconds.1

This system of patterned lights, along with other types like flashing lights and occulting lights, is regulated by international agreement to ensure clarity and safety for maritime navigation. The term "flashing" itself can also refer to any light that shines at regular intervals, or more broadly, to emitting bursts of light or presenting something for attention.12