APPENDIX 



55 



straight line joining these two points on the 

 chromaticity diagram is the locus of all color 

 combinations resulting from the mixtures. 



Measurement of Sensations 



The measurement of sensations is an interesting 

 area of research which has hardly been investi- 

 gated by psychologists. Many physicists doubt 

 that sensations can be measured, but orderly and 

 systematic work in this area is possible. As 

 evidence of this, we may cite a very recent study 



of the test area which looked half as bright. 

 Three things are evident from this figure: (a) 

 the results obtained with the different colors 

 seem to agree with each other, (b) the agreement 

 among the various points is almost as good as one 

 gets with photometric measurements, and (c) a 

 luminance which is half another luminance does 

 not necessarily look half as bright. 



The data cited above are preliminary, but they 

 hold great promise for quantification in an area 

 where it was once thought impossible. More 



X- PERCENT OF RED 



Fig. 45. The I.C.I, chromaticity diagram for plotting the locations of colors in terms of the percentage 

 of standard red and green in red-green-blue mixtures required to match them. 



on the relationship between luminance and 

 brightness. 



The Relationship Between Luminance and 

 Brightness . In this study (33) each observer was 

 required to adjust the luminance on one test area 

 until it looked e.xactly half as bright as another. 

 None of the observers expressed any doubts about 

 being able to make these fractional judgments of 

 brightness nor did the nature of the judgments 

 seem unnatural or artificial to them. They were 

 also able to make these judgments with con- 

 siderable consistency. 



The results of this investigation are shown in 

 Fig. 46. The abscissa shows the luminance of 

 the standard test area, the ordinate the luminance 



work is under way to explore more fully still other 

 parameters in connection with this function. 



Chromaticity and Color Sensation. It is now 

 known that equal distances on the ICI chro- 

 maticity diagram do not represent equallj' notice- 

 able color differences. This is another way of 

 saying that color sensation does not keep pace 

 with chromaticity. Data on this point come 

 from a study by MacAdam (63), who investigated 

 chromaticity differences which could just be 

 perceived by the eye. His data are shown in 

 Fig. 47. The distances from the center of anj^ 

 ellipse to the boundary of the ellipse represent 

 equally noticeable color differences. Actually, 

 the ellipses in this figure are magnified 10 times. 



