For the human being, visual perception is determind by and interaction between light, object, eye and the brain. But in the colorimetry instrumentation, we find the familiar elements of the triplet, but the light source is replaced by a lamp and filters. The object stays the same. An analyzer system, or a unit with a monochromator combined with a detector, simulates the eye and the observers. A support and sample-holder are used to position the object, and an appropriate measurement geometry determines how the sample will be lit and observed by the measuring instrument. An electronic processing unit or computer replaces the brain of the observer and performs all the colorimetric calculations.

The Light Source
Modern colorimeter and spectrophotometer devices normally use one of two types of light sources: halogen-tungsten lamps or xenon lamps.

The Detection System
The "eye" of the colorimetric measuring instrument is different in tristimulus colorimeters and spectrophotometers. In the case of tristimulus colorimeters, three or four interference filters are matched with silicon detectors. The combination of their respective characteristics generally allow the color matching functions (x,y,z bar) of the everage human observer to be simulated correctly for daylight. On the ohter hand, spectrophotometers use some type of monochromator system, to dispense and select light, combined with a detector, to analyze the visible spectrum os the sample. There are two type of monochromators systems in use: interference filters and diffraction gratings.

The Object
The measurement geometry determine the angles of illumination on the sample, and the angles of observation for the measuring instrument. There are two types of geometries in common use: the 45/0 degree (or 0/45 degree) geometry and the diffuse/0 (or 0/defuse) geometry.

Spectrophotometers with 45/0 degree geometry illuminate the sample at an angle of 45 degree, and measure perpendicularly to the surface (with the reverse in the 0/45 degree). Instrument with the 45/0 degree geometry analyze diffuse reflection only, and in general observe the object in conditions similar to natural observation of colors and objects by human. This means that the instrument analyzes only the color generated by the coloring material in the object (less the gloss). The measurements are always made without the specular usinbg 0/45 degree geometry.

Spectrophotometers with  diffuse/0 degree geometry illuminate the sample in a diffuse manner, and then observe at 8 degree from perpendicular. The specular energy component (gloss) is typically included in the measurement, meaning that the measurement includes the color due to the coloring material in the sample and also the gloss of the object, which is related to the physical and geometrical characteristics of the object surface. Most of the spectrophotometers with diffuse/0 degree geometry offer additional capability of measuring transmitted light in the case of transparent or translucent samples.

In addition, this geometry is frequently equipped with a spectrophotometer used to remove or include the specular energy component (excluding gloss or including gloss).