Abstract
The experimental apparatus used of three gas-filled tungsten lamps, three glass filters and a flashed opal glass. The flashed opal glass was illuminated by three colored lights actuated by the three lamps in conjunction with the three filters. The transmitted light through this glass was the stimulus light. The distance between the surface of the flashed opal glass and each of the lamps could be varied continuously by means of a driving motor.
The chromaticity and the luminance of the stimulus light were calibrated by a spectrophotometer, a phototube, etc. The positions of the two of the three lamps were fixed so that the locus of the stimulus light was straight on the chromaticity diagram and the luminance in the white sensory region was about 20 abs. The observers changed the position of remaining lamp by the method of minimal changes to determine the white points.
The results are summarized as follows.
1) The white points were determined which could be judged white with a probability of 0.5 by three observers experienced in color experiments, and the white sensory region was obtained from these white points by elliptical approximation. It was found that the white region varied in position in the different observers, but for every observer, it was located below the black body locus. This is different from a common opinion that the central point of white on the chromaticity diagram is the chromaticity coordinate of the C. I. E. standard source C. In the experiment, the light of the C. I. E. standard source C was recognized frequently as white only by one of the observers.
2) The white sensory region which was judged at least as white by any one of the three observers was a rather broad zone along the downside of the black body locus (color temperature 4, 500°K to 25, 000°K).
3) The white sensory region which was judged at least once as white by an observer inexperienced in color experiments was very wide and presented an approximate ellipse having the normal line on the black body locus (color temperature 4, 500°K to 30, 000°K).
4) When the surrounding field was illuminated by a red light or a green light or a blue light or a tungsten lamp, the white sensory region moved towards the chromaticity of the adaptation field in all the three experienced observers.
5) When the white judgement was made arbitrarily only in each experiment, the variation was 0.007 to 0.02 on the x-y chromaticity diagram. When the same judgement was made ten times in each experiment for a given time, the variation for the time was 0.004 to 0.008.
