WOptical phenomenaWAdularescenceWArs Magna Lucis et UmbraeWAsterism (gemology)WAventurescenceWBest Illusion of the Year ContestWBlack drop effectWBlue field entoptic phenomenonWChatoyancyWEinstein ringWExtinction crossWFermat's principleWFörster resonance energy transferWGegenscheinWGlobe effectWGoos–Hänchen effectWHelmholtz–Kohlrausch effectWHidden faceWIridescenceWLabradoriteWLens flareWLight leakWList of optical illusionsWLowitz arcWOpalescenceWOpposition surgeWOptical illusionWShadowWShadow blister effectWSurface plasmon resonanceWTotal internal reflectionWTyndall effectWUmbra, penumbra and antumbra
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