HOW MUCH PHYSICS DOES COLORIMETRY REALLY NEED

This contribution tries to expel the Dunwich Horror of ''undimensioned '' tristimulus values from colorimetry. I intend to show that tristimu lus values have units, and that we may attribute a common dimension to these units. Colorimetric units are independent of physical units. Th ey are sets of primaries, determined by directions and relative length s in color space but without definition of an absolute length, because in colorimetry quantities generally refer to ''reference stimuli.'' C olor-matching functions can be defined as tristimulus values of monoch romatic stimuli. To define them as Mr. Brill does in his Definition 1 is possible and consistent, but it does not correspond to the use of t hese functions in colorimetric practice. And it leads to inconsistenci es if color-matching functions are interpreted as having the units wat t/watt. (C) 1997 John Wiley & Sons, Inc.