The moiré effect lights that guide ships home

I'd never heard of moiré effect beacons until I got an email asking me about them. It seemed like a really clever idea - but it was really hard to research. Or at least it was, until I stumbled upon one magic phrase that revealed its history.

It turns out this thing's called an "Inogon leading mark" or "Inogon light" -- Inogon, not Inogen -- and it's a Swedish invention from the 1980s. But there's still a question: why is being used to mark an undersea cable, instead of guiding people home?

(Full disclosure: there were some weird strobing effects from the light that only showed up when I got the footage into the edit, so the image you see here has been digitally stabilised so it appears the same way on screen as it does in person!)

Thanks to Andrew Stine for suggesting this!

References:
The original Wikipedia article: https://en.wikipedia.org/wiki/Moir%C3...
The patent: https://patents.google.com/patent/US4...
The US military analysis [PDF]: http://www.dtic.mil/dtic/tr/fulltext/...

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