It's difficult to research something if you don't know the name of it. I got an email a few days ago asking if I could figure out anything about this. And normally, I try to discourage messages like that, I'm not Google and I'm not a reference librarian, but this thing completely nerd-sniped me. Because other than one reference on Wikipedia to this exact light that's for shipping on Southampton Water, I couldn't find anything about it. Which is weird, because this is a really clever idea.

This light is based on moiré patterns, which are the extra lines and patches that seem to appear when you have two similar but slightly different patterns overlaid on each other. You see them in a few places, but most of the time they're confusing and distracting and designers want to avoid them. But here, the patterns are set up so that if you're looking straight at that light, dead on, you see parallel lines.

But if you're to either side, the arrows formed by the moiré patterns tell you which way to go to be straight-on to it. You can have five different boats in five different locations out there, all looking at the same sign, and they will all see arrows pointing the right way for them, without any computers or fancy tracking. This seems like such a good idea that I couldn't believe it wasn't well-known. So I went searching.

"Moiré shipping light." "Moiré boat light." And after a half hour or so, I'd found a couple of others around the UK, placed at the entrances to locks and marinas, or at the end of dredged channels, so that people steering a boat know exactly which way to go to avoid the sides. One guide for mariners called it an "Inogen light" but that just led me to a medical company, nothing else. And that was it. It looked like a bit of weird maritime history

that had been a brief fad and then died out, leaving no trace. A beautiful idea that the world had ignored. I considered starting a new series of videos called "I Don’t Know" just to see if anyone knew more about it, because it's genius and, yeah, I wanted to understand it. So much that my brain wasn't quite done, I kept coming back, I kept searching. And eventually, I started looking through patent databases. And after a few minutes, I found it.

It was patented by Lars Bergkvist and Ivan Forsen, from Sweden, in the late 1970s. They'd invented several things to do with moiré patterns, between them. And though there are a few more patents after the first, refining the idea or making it work in two dimensions with circles, the trail ended there. I tried to track Lars or Ivan down, and couldn't find any trace. The only thing I had was an address from about forty years ago.

And in Sweden. And then one little clue, spotted just out the corner of my eye, unlocked everything. Yes, this was patented by Bergkvist and Forsen, but the patent was then assigned to a company called Inogon. Not Inogen -- that was a typo, or a corruption of the name over time. Inogon. This is known as an Inogon leading mark, or just an Inogon light. And once you know that, once you name it, you can search for it.

You can find the US military analysis from 1986 testing that it works. The variations that were made for getting an aircraft into the right place parking in a stand. The Swedish company called FMT that now makes them, or did until recently, because they've just removed it from their web site. Once you know that this is an Inogon light, all the rest of the research becomes easy. All except one thing.

This Inogon light isn't being used to guide people in. The light follows the path of an underwater cable where you shouldn't drop anchor. So the signal here is all wrong. You don't want to follow these arrows, you're required to stay away from them unless you're passing straight through. It's a really weird use for a very expensive light. So why is it here? I don’t know. But if anyone out there does know, for sure, with evidence...

do get in touch.