The position index of a glare source at the borderline between comfort and discomfort (BCD) in the whole visual field

The objective of this study was to propose a new position index for a source located in the whole visual field, including the lower visual field. The sensation of brightness was tested at various positions in the visual field. The Glare Tester especially designed for and used in this experiment had two sources: the standard source located on the line of sight and the test source located at a designated position in the visual field. The boundary of the visual field, BCD luminance on the line of sight, and BCD luminance at various positions in the visual field were measured. The visual field was measured, and the boundaries were approximately 90° temporally, 67° inferiorly, and 50° superiorly. From the measurement of BCD luminance on the line of sight, the BCD luminance was obtained at 2590 cd/m2 under the conditions of a source size of 0.0011 sr and background luminance of 34.3 cd/m2. In measuring BCD luminance at various positions, the standard source was set to the BCD luminance of each observer, with the luminance of the test source being increased. The observers were asked to stop when the sensation of the test source became equal to that of the standard source. From the results of these measurements, the position index Pi was derived. Finally, a chart for determining the position index Pi was proposed based on the three measurements.