The effect of a small, intense glare source (118 dB) on the brightness of a small target was measured as a function of glare angle and target luminance. Using an interocular matching procedure the observer adjusted the brightness of a match field (seen by the right eye) to equal the depressed brightness of the target under the influence of the glare (seen by the left eye). Glare angle was varied from 13-2 to 274 min. Target luminance was varied from 58 to 93 dB relative to 10-10 Lambert. For all target luminances, the apparent brightness of the target was shows to be directly related to the logarithm of the glare angle. At a given glare angle the brightness grows as a power function of the luminance, and the exponent of the power function is largest when the glare angle is smallest. In double logarithmic coordinates the functions relating the luminance of the match field to that of an equally bright target become straight lines that converge at a common point, equal to the luminance of the glare (118 dB).
Abstract