Light Source Size and the Stimulus to Vision

Abstract

Non-luminous objects present a stimulus to vision that depends on their optical interaction with the sources that illuminate them. "Sources" in this context means all other objects, as may be seen if the main object of interest is a plane mirror, or a mirrored sphere, for example. Such examples show that contrast in an object can depend on contrasts elsewhere in the environment. An important and highly variable feature of the optical environment is the size of the primary light source. This paper will look at light source sizes and their effect on the appearance of shiny objects. (Obviously, source size affects the appearance of matte objects also.) Table 1 shows that familiar lights vary in the bright solid angle that they present by a factor of 105 or 106.