Among the earliest photoelectric color-measuring instruments
were those in which the source-filter-photodetector
combinations duplicate the tristimulus functions of the Standard
Observer and a CIE Standard Illuminant, usually Illuminant
C [29]. How well their filters are designed and matched
to the spectral characteristics of the source and of the detector
determines how accurately the instrument performs. Today
a high degree of accuracy is attained in the resulting
tristimulus values.
Because of their ease of operation, good precision, and
relatively low cost, tristimulus (filter) colorimeters have
found wide application for industrial control. They are used
primarily as color-difference meters to evaluate the difference
in color between a production specimen and a standard
of similar spectral character. This last limitation is important
for most colorimeters. Because of their design, most colorimeters
provide colorimetric data for only one combination of
illuminant and observer and therefore cannot detect
metamerism. When specimens are metameric, a colorimeter
can give incorrect data on the differences among them. Filter
colorimeters should not be used to evaluate pairs of specimens
that may be metameric. This limitation should be
clearly understood.