Comment by dbuxton
20 hours ago
Many runways have something called PAPI (precision approach path indicator) which does something similar. Basically you have four (or two sometimes for less precise version) lights which appear either red or white depending on whether you are high or low on the glidepath and you aim to get two reds and two whites - more whites means too high, more reds too low.
I can see that this would be not very intuitive for left/right guidance but are similar systems used in ship navigation?
Yes - sector lights. When you are on a channel / in safe water they’re white, red in the port sector, or green when you are too far starboard. Some will combine this with an angle dependant flash to alert you how far into a port or starboard sector you may be.
The other common mark you’ll see are leads which are two lights, one behind the other. The front is lower and the rear is higher. When they’re aligned you’re on the channel. These also have day shapes attached that provide an upwards and downwards facing triangle to align.
It is used and I guess it works largely the same way as in author’s first picture: you get arrows pointing towards where you should correct your course to. Tom Scott has made a video on those: https://wew.youtube.com/watch?v=d99_h30swtM