Land effect

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A vivid impression of a full range of colours created from monochromatic light. The effect is produced by taking two black-and-white photographs of a coloured display such as a bowl of fruit, the first with a green filter over the camera lens and the second from the identical position with a red filter, and then superimposing images of the two resulting black-and-white transparencies on a screen with slide projectors, the first without any filter over its lens and the second with a red filter. Although in terms of absolute wavelength all the light falling on the screen and being reflected from it is red, pink, or white, apples look green, plums blue, bananas yellow, and so on, disproving the common misconception that the colour of an object in the visual field is fully explained by the wavelength of the light reflected from it. In reality, the visual system assigns colours according to the relative balance of short, medium, and long wavelengths across the whole visual field, so that light of a particular wavelength has no inherent colour in itself but may be perceived as any colour depending on the range of wavelengths in the surrounding visual field, and this is why the effect disappears if the screen is viewed in void mode. See also colour constancy, cone, retinex theory. Compare Gelb effect, Kardos effect. [Named after the US physicist Edwin H(erbert) Land (1909–91), inventor of the Polaroid Land camera and president of the Polaroid Corporation, who discovered the effect and published it in the Proceedings of the National Academy of Sciences in 1959 and in Scientific American magazine later in the same year]

Subjects: Psychology.

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