What can pictorial artifacts teach us about light and lightness?

The virtual collection of human pictorial artifacts represents a treasure for vision scientists: they are not only a showcase of possible — even if often improbable — visual experiences, but also a showcase of visual indexes and information employed by the visual system to generate our phenomenal world. In this work, we address three possible lessons that can be derived from the study of pictorial artifacts, related to the experiences of light and achromatic surface color. The first addresses the definitions of the words lightness and brightness; the second lesson is about the interactions between light and lightness; the third is about the visual experience of light and how artists managed to represent such experiences.