GoKawiilI was inspired by Tom Scott’s excellent video and links here https://www.youtube.com/watch?v=d99_h30swtM
where he talks about a particular type of “Inogon” light used to guide ships through channels or harbours.
The patent is here: https://patents.google.com/patent/US4629325 and the military report on the effectiveness is here: http://www.dtic.mil/dtic/tr/fulltext/u2/a168108.pdf
(Hint; They don’t seem to like it much).
I decided to build my own to play around with the effect. After a few minutes sketching in inkscape and a few more lasercutting, I had this:
I followed the claims in the patent fairly closely. They advocate between 1.5 to 1.8 ratio of pitch spacing to the width of the dark bands, and I used 1.65 (this yields a mask with a ‘duty cycle’ of around 40%), and to use only a single excess band on the first mask relative to the second.
Here’s what it looks like when illuminated from the back, and dead-on to the beam:
(There’s some minor circular effects because the separation of the two grids is significant compared to how close I’m standing. If this was on a riverbank and I was 100m away, that’d disappear)
Here’s what it looks like from various angles:
Am I happy with it? You betcha. It does exactly what it says on the tin. It’s a intuitive and nifty way to guide a vehicle, requires very little ‘calibration’, and can cope with a dozen or more people using it at the same time without any problems.
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