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Light can play tricks on the mind. Two people can perceive the colour of an object very differently, depending on how they are viewing it. For instance, if you go into a room that is illuminated blue, the cone receptors on your retina compensate within 10 to 15 seconds, making the blue appear less intense. If a second person enters the blue room, it takes time for their retina to adjust so they will, at least for a short time, have a different colour experience from you. Alternatively, if the lighting is suddenly changed from blue to white, everything in…

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