Analysis of Human Color Vision by Exchange Thresholds

Abstract

A property of vision that is particularly useful in the analysis of color vision is called “The Principle of Univariance”. It was already implied in Thomas Young’s formulation of trichromacy. Somewhat loosely expressed, it means that the response of a visual receptor depends upon the number of quanta it catches but not upon the wavelength of these caught quanta. Rhodopsin, for example, absorbs green light more readily than red, thus green light will excite the rhodopsin-filled rods more than will an equal energy of incident red light. But if, instead of measuring the energy of light incident, we measure the energy absorbed, then it is found that red and green lights that are equally absorbed will have identical rod-exciting effects, and will hence appear identical by rod vision.