Farbfilter, Farbenblindheit und Farbensehen

Summary

A green-blue filter placed before the eye produces red-green colour blindness, a purple filter a green-red colour-blindness, an orange filter a blue-yellow colour-blindness. These artificial absorptive visual defects have great similarity with the naturally occurring forms of colour-blindness (proto-, deutero-, tritanopy and anomaly and display typical confusions of colours, exaggeration of brightness differences and of simultaneous contrasts, and great dependence of the chromatic impression upon strength of illumination and size of field. The similarity is based on the fact that the filter cuts out approximately that range of colour for the normal eye for which the colour-blind eye possesses no photochemical receptor in the retina. The simple experiments, which can be demonstrated not only by placing a colour filter before the eye, but also by means of coloured illumination produced in a dark room, permit us to understand why an absorptive or receptive visual defect never results in redblindness or green-blindness alone, because the general chromatic tone of the visual field is confused with white, and enable persons with normal colour vision to feel how the colour-blind see colour. The experiments are related to the general theory of colour vision with special reference to the photochemical data on sensitizing pigments decomposed by light and to central nervous regulation (antagonistic effects in reciprocal innervation).