When we interpret a shaded picture as a three-dimensional (3D) scene, our
visual system often needs to guess the position of the light source in order
to resolve a convex-concave ambiguity. For more than a century, psychologists
have known that the visual system assumes that light comes from above and
have argued that this assumption is ecologically justified because our everyday
light source (the sun) is overhead. Our experiments reveal that people's preferred
lighting direction is not directly overhead, but rather shifted to the left,
and this preference is reflected in art spanning two millennia. Furthermore,
we find a strong correlation between people's handedness and their preferred
lighting. We suggest that what counts is not so much where the sun is, but
where you like the sun to be.
