What does the character of a lighthouse light tell navigators?

The character of a lighthouse light serves as a unique identification signal that allows navigators to distinguish one lighthouse from another. By rhythmically flashing or eclipsing its light in a specific, internationally regulated pattern, a lighthouse provides a reliable visual code that mariners can cross-reference with official Lists of Lights to establish their position.123

These patterns, known as the character of the light, include several distinct types:

• Flashing lights: Display a single flash or groups of flashes (e.g., two, three, or four) repeated at regular intervals.1
• Occulting lights: Normally remain on but are momentarily extinguished at intervals.1
• Isophase lights: Alternate between flashes and eclipses of equal duration.1
• Fixed lights: Burn steadily without flashing or eclipsing, often used for directional guidance in harbors or to mark specific channels.1

The interval at which a pattern repeats is called the period. Because these signals are simple and reliable, they remain a vital tool for coastal navigation, providing essential reassurance and a backup to electronic systems.12