The Paris Effect: A Tale of Eccentricity

Differences in color perception as a function of eccentricity have been studied in the past, especially due to variations of macular pigment in the retina and of cone pigment density. However, such differences have been observed under laboratory conditions and this property of the human visual system is not pronounced under everyday conditions. This paper presents an example of a strong effect that was observed at the 31st Color Imaging Conference in Paris when viewing its stage layout and lighting under the overall environmental conditions of the conference hall. In particular, multiple chromatic purplish-violet focus lights were directed at the stage wall. When focusing on one of the lights’ reflections on the stage wall, the other lights to the left or right appeared to have a significantly different, duller and cooler color appearance. The effect was immediate and robust to focusing on any one of the chromatic lights, with the others appearing different at the periphery of the field of view. In order to understand the effect, an attempt was made first to reproduce it using common LED torches coupled with colored gel filters and a pilot psychophysical experiment was performed. The filtered LED light sources were then also measured for a variety of filter colors and simulations were performed, first with differences between 1931 and 1964 color matching functions and then using a cone sensitivity model that allows for predicting the effect of varying eccentricity. This led to the finding that the effect can be measured and expressed at least qualitatively using existing tools, with simulated colorimetries showing the correct direction of shift from warmer more vibrant to cooler, duller colors. We call this the “Paris effect” in honor of the location where we observed it and Paris being the “city of light”.