A Psychophysical Study of White II Neutral Adaptation Area and Duration as Variants

Experimental data are presented which provide a psychophysical specification of white in terms of color temperature, luminance, stimulus area, and duration. White threshold contours for three observers were obtained for five different angular sizes of test field: 2.0°, 5.8°, 11.7°, 23.4°, and 46.8° subtended at the eye, and for two exposure durations: 1 second and 5 seconds. The luminance range extended from 3 mL to 3000 mL. All results were obtained for a neutral state of adaptation. The specific variation in the white threshold with changes in stimulus area is itself shown to be a function of the color temperature of the test stimulus. The major effect of an increase in stimulus duration is an increase in the range of color temperatures which appear white at a given level of luminance. Sources of inter-observer differences are discussed, and the variability of the measurements is shown to be lawfully related to the luminance level.