Two kinds of such colorimeters can be found:
Colorimeters made of one single detector and a filter wheel. The latter comprises three filters, whose transmission spectra are equal to the colorimetric functions , and . By spinning the filter wheel, the three filters are then periodically set in front of the detector.
Colorimeters made of three different photodetectors, working simultaneously, having spectral sensitivities equal to the colorimetric tristimulus functions.
In both cases, the trichromatic components of a sample are measured after calibration with a reference source whose spectrum is close to the spectrum of a normalized illuminant. These colorimeters are in general less accurate than those based on a monochromator (see below).