How does an isophase lighthouse light alternate between light and darkness?

An isophase lighthouse light is a specific type of signal characterized by its rhythmic pattern of illumination and darkness. Unlike other light characters that may feature varying lengths of flashes or eclipses, an isophase light alternates between periods of light and darkness that are of exactly equal duration.12

This rhythmic consistency is part of the character of the light, which allows mariners to identify specific lighthouses at night. While other systems, such as occulting lights, remain primarily on with brief interruptions, or flashing lights, which remain primarily off with brief pulses, the isophase light provides a balanced, repeating signal that helps ensure safe coastal navigation.1