The paper addresses the following problem: Given an array of light intensities obtained from some scene, find the light sources in the original scene. The following factors are discussed from the point of view of their relevance to light sources detection: The highest intensity in the scene, absolute intensity value, local and global contrast, comparison with the average intensity, and lightness computation. They are shown to be insufficient for explaining humans' ability to identify light sources in their visual field. Finally, a method for accomplishing the source detection task in the mondrian world is presented.
