Brightness Discrimination Data for the Specification of Quantity of Illumination

There is abundant experimental evidence revealing that different visual tasks require different levels of illumination. Thus, specification of the quantity of illumination for a particular lighting installation requires diagnosis of the visual task involved and application of appropriate visual performance data. It is here proposed that ultimately the specification of quantity of illumination from performance data should be based upon systematic data representing the relations between speed and accuracy and illumination for various fundamental visual tasks. Once such a body of data exists, the illuminating engineer need only develop a method for diagnosing the appropriate set of data for fundamental visual tasks to apply to the actual visual task at hand. At the time of writing, it seems likely that satisfactory methods of diagnosis of visual tasks will be developed, in the form of visibility or contrast meters.

The present paper reports a set of experimental data which were collected to provide a basis for specifying the quantity of illumination, when the visual task is that of discriminating brightness differences. Separate measures of speed and accuracy of brightness discrimination have been obtained for each of a number of illumination levels. Methods are suggested for utilizing these data to specify the necessary quantity of illumination for various levels of speed and accuracy.