Assessing the Fitness of Visual Pigments for their Photic Environments

Abstract

In the dictionary sense a pigment is a substance that is coloured to the human eye. Colour is so striking a sensation that it was once thought to be an attribute of the “coloured” substance itself. The appearance of an object, however, depends not only on the inherent properties of the object, and the sensorium of the organism that perceives it, but on the nature of the light that illuminates it. In a certain respect, however, we can relate the colour of a substance to a physical attribute, and that is by its absorption spectrum. This is a mathematical concept expressing the variation with wavelength of the ability to absorb light. Apart from white, grey and black pigments, which absorb all wavelengths equally (the white not at all, the grey a constant fraction, and the black completely) pigments absorb light selectively and characteristically.

The eye may be said to owe its existence to light, which calls forth, as it were, a sense that is akin to itself; the eye, in short, is formed with reference to light, to be fit for the action of light; the light it contains corresponding with the light without.

Goethe