Luminance Difference Threshold under Adaptation Luminances Differing from the Luminance of Background of the Object to be Perceived...Re-survey of Holladay's Principle

Abstract

A survey of visual performance is essential in determining lighting requirements.In this connection, a great number of investigations on the luminance threshold have already been carried out for various experimental conditions.In most of these experiments, however, visual field was uniform except for the test object and the observer's eyes were adapted to this uniform luminance.In practice, most visual fields are non-uniform and the observer randomly scans such a field with his eyes.Then, the adaptation luminance of the observer's eyes does not always coincide with the luminance of background of the object.The luminance threshold obtained in the experiments above mentioned, therefore, can not directly be applied in most of practical visual conditions.The Holladays principle is well known as a way to deal with luminance threshold under conditions where the adaptation luminance of the observer's eyes is not equal to that of the background.This principle, however, was obtained from experiments with one or more concentrated glare sources.This implies that the Holladay principle can be applied also to other non-uniform visual fields but leanes still some uncertainty in its application.To extend the validity of the Holladay principle to more general conditions, the luminance thresholds were investigated for conditions combining various background luminances (Lb) of the object with the luminances (La) to which the fovea of the observer was adapted, under the conditions of La >> Lb.As a result, it was found that the state of the foveal adaptation of the observer's eyes can be represented not by the luminance contrast threshold but by the luminance difference threshold. This finding was in fairly good agreement with the Holladay principle.