A project to measure visual performance at mesopic light levels has recently been completed. An empirical relationship between visual search time and the photometric characteristics of a target and background has been developed on the basis of experiments with 15 subjects. This search time model has been submitted for consideration by the CIE as a new metric for predicting visual performance. The photometric characteristics of the target and background require measurement using standard CIE photopic and scotopic responses. Examples are presented of potential applications of this measurement technique.
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