How this Navigation Light Uses the Moiré Effect to Guide Ships Home

The little-known moiré effect is the basis of this marker that helps mariners navigate hazards in port or close to shore. In this video, the host explains this effect and poses the question: why, in the case of Southampton, is a moiré effect beacon, aka an inogon leading mark, used to mark an undersea cable to be avoided instead of guiding people home?

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