Fictitious optical illusions? Hardly! These have a physical meaning. These are examples of Moire’s Patterns. Moiré patterns appear when superposing two transparent layers containing correlated opaque patterns. The case when layer patterns comprise straight or curved lines is called line moiré. In simpler words, when you have two mesh and you allign them with some angle between their wires, you tend to find certain patterns, made by light. If you change the orientation, this pattern changes accordingly. You may also have seen this effect in certain pictures and paintings, like the ones below:
In these cases, the texture of the surface of the photograph or the canvas on which the painting was made, has certain elements such as fibre-lines, superimposed over layers, that lead to light interfering in a particular manner to give us these patterns.
But for those of you who are optimists and like to see the silver lining in this case, when all the Moire pattern seemingly do is spoil your favorite painting and photographs, there’s good news: these patterns can be extremely useful. For one, they can be used to estimate the dimensional change and resultant strain in a particular structure or configuration. All the analyst needs to do is to try and generate Moire patterns by laying the actual photograph after the strain has been developed with a reference photograph of the initial structure/configuration before the strain was experienced by the entity.
Did you know that our currency notes have Moire patterns too? Rather our bankers have made them such so that when digital scanners scan the notes, the Moire pattern analysis is seen as an essential test for cases of counterfeit notes. In fact Moire patterns are so useful in checking such wrong practices that we have something known as a Kan’t Kopy Paper as well, which is basically a type of security paper printed with patterns that cause these patterns to be formed. Most importantly, these patterns are usually unique and patented by the organization administering the movement of these notes and KK papers.