A constant appearance is essential for a variety of products. Colour measurement as part of quality assurance is now indispensable. Design and colour play a very important role and must be repeatable and controllable.

The colour comparison with the human eye is subjective, every person sees, tastes and smells different. Spectral color measurement replaces subjective perception with an objective measurement.

Colours are basically described by the three variables:

Hue
Basis of color perception

Chroma
Colour saturation from bright brilliant to colourless.

Iluminance
Description of the colour from bright to dark.

A spectrophotometer measures colours by illuminating the sample and analysing the light that is diffusely reflected. The resulting spectrum is compared to the spectrum of a known (normally white) surface and the spectral characteristics of the measured surface are calculated. This sample spectrum is then weighted with a standardised illuminant, for example for daylight (D65), and with the three spectra (colour matching functions 10° or 2°) derived from the human perception.

This results in three values X, Y and Z which are not only dependent on the used illuminant (D65) but on the colour matching functions, 10° or 2°.

This sounds complicated but it is not; most industries use the same basics settings D65 illumination and 10° standard observer, which are setup and left. Colour differences are normally described by adding the differences of the three colour values (mainly CIE Lab) together, resulting in a single value delta E (DE).