APPENDIX 



45 



magnitudes of our sensations have been developed 

 by psychologists, and the sensation magnitudes 

 obtained are not the same as those which result 

 from the measurement of light and color. 



Comparable Concepts in Phrjsics, Psychophijsics, 

 and Psychology. It is instructive and helpful to 

 list parallel concepts which have been suggested 

 by the OS A Committee, and Table II has been 

 adapted from the committee's report. This is 

 not a complete listing of concepts, since there are a 

 number of others for measuring radiant flux and 

 luminous flux which are not given here (see 

 Table III, however). Three important points 

 about this table are (a) that there are some blank 

 places in it, i.e., there are no terms for certain 

 attributes of our sensations to match character- 



distinction somewhat more clear. It is possible 

 to get a piece of blue paper which will match the 

 blue of the sky in color. The blueness of both 

 the sky and paper is a relatively simple aspect 

 of our inner experiences and is called a sensation. 

 But the sky does not look like the paper. The 

 sky has a filmy, rather transparent appearance, 

 while the color of the paper appears to reside in a 

 surface. These "modes of appearance" are more 

 complex than our sensations and they have been 

 called perceptual attributes. Glossiness, lustre, 

 transparency, sparkle, etc., are perceptual con- 

 cepts. They have not been listed in Table II 

 because they do not, in general, parallel the other 

 three types of concepts. The perceptual concepts 

 are the least well understood of all those we have 



TABLE II 



Some Parallel Concepts Relating to Light and Color 



Adapted from a Report by the Committee on Colorimetry of the Optical Society of America (16) 



istics of radiant energy and light; (b) certain 

 new terms have been introduced, e.g., chromatic- 

 ness, luminance, illuminance; and (c) the term 

 brightness has been reserved to refer to that 

 attribute of sensation which corresponds most 

 closely to the physical and psychophysical con- 

 cepts of radiant and luminous flux. 



Perception. There is still another class of 

 concepts which, the OSA Committee recognizes, 

 relate to our experiences of light and color. 

 These are the perceptual concepts. They, like 

 the concepts relating to sensation, fall entirely 

 within the province of psychology. Psychologists 

 are not entirely agreed on the differences between 

 sensations and perceptions, but in a general kind 

 of way the two terms are useful in distinguishing 

 between the relatively simple, as compared with 

 the relatively more complex, attributes of our 

 inner experiences. An example might make the 



discussed here. At present, psychologists have 

 done little more than to classify some of these 

 perceptual elements and to study some of the 

 conditions which are necessary for their appear- 

 ance. Little quantitative work has been done in 

 this area. 



With this as a background, we may now proceed 

 to examine the kinds of measurements which 

 may be made on visual stimuli. 



Radiometry 



Radiometry is the measurement of radiant 

 energy in purely physical terms. The instru- 

 ments, techniques, and units of measurement in 

 radiometry have all been carefully standardized, 

 and there is good agreement among physical 

 scientists about them. They are difficult meas- 

 urements to make, however, and this probably 

 accounts for the fact that so few visual studies 



