Occulting

Light that goes dark

An occulting light is the opposite of a flasher — it stays on, and briefly blinks out. A steady light that pauses, on a fixed rhythm.

How to read it

Oc 4s      on 3s, off 1s
Oc(2) 8s   two short eclipses
steady     mostly on, barely dark

Why they matter

Occulting lights mark spots where a fixed light would blend into shore lights. The blink-out is the signature — subtle, but unmistakable once you know it.