On Equivalent Sphere Illumination

Abstract

Under the present equivalent sphere illumination (ESI) system, the actual visibility of a visual task is not known. The author recommends that for every different task and viewing angle, the maximum contrast sensitivity of the task be published; thus, one can determine the ESI required for any given task in order to achieve a certain visibility, or one can obtain task visibility by knowing its ESI value. This broadens the application of the ESI system by enabling conversion between ESI and visibility for a specific task and also conversions among different tasks and viewing angles. Moreover, differences in individual contrast sensitivity response may result in different ESI and visibility from the same task, with the same viewing angle, at the same location under the same luminous environment.