In 1982, engineers came up with the Inogon Leading Mark, a clever solution to guide ships into a harbor without using any electronics. The Inogon light makes use of the moiré effect, creating an optical illusion of arrows that change direction based on the angle they are viewed from. This unique use of distortion in overlapping lines ensures that ships always know which way to go without any confusion. The Inogon Leading Mark is a fascinating application of optical effects that is both surprising and effective, making it a remarkable innovation in navigation technology. Source: Tom Scott.
https://www.popularmechanics.com/technology/infrastructure/a19091534/inogon-leading-mark-moire-effect-light/