Color meters and optical instruments can only be one part if you need to compare colors and substrates. Since no technical device is as precise as the human eye, the visual color control is essentail for your quality control.
It is written in the ISO 3668:2009 standard how to assess colored substrates in manufacturing industries (automotive, plastics, furniture etc.). On the contrary, visual color machting in the graphic arts industry is described in the standard ISO 3664:2009.
|ISO 3664:2009||ISO 3668, DIN 6173-2, DIN 5033|
|Graphic technology and photography – Viewing conditions||Visual comparison of the colour of paints|
|Illuminant D50 (CIE)||Illuminant D65 (CIE)|
|Graphic arts industry||Manufacturing industry|
Reproducible conditions are necessary for standardized and repeatable color matching processes. Natural dalight would be a good starting point for the light quality but the light spectrum varies depending on time of day and place. Therefore, for uniform viewing conditions color matching boxes with artifical CIE daylight D65 are used.
The requirements for a viewing booth and its lighting are defined in ISO 3668 and are fulfilled by all our Color Viewing Light cabinets:
In order to standardize not only the viewing environment but also factor „human“, special requirement are placed on the observer. The observer must be perceive color normally and should have experience in color comparison as well as a good ability to distiguish different colors. Corresponding visual tests help to choose suitable observers. In addition, a neutral color such as gray must be worn during the color assessment.
Two-dimensional sample plates need to be viewed with illumination of 0° by a viewing angle of 45° (measuring geometry 0°/45° and 45°/0° respectively). Howeder, certain application fields require different viewing and illumination angles, that is why appropriate sample holders are available in the web shop.
Color differences are indicated to the ISO rating scale by hue, chroaticity and brightness. Finally, all details of the color matching procedure should be recorded in an assessment report. A corresponding function to create such reports is available with the PROFESSIONAL series of the Color Viewing Light booths.
For the detection of metamerism, means two color samples that appear equal with one illuminant but looks different with another light, the substrates must also be assessed by CIE-illuminant A (incandescent lighting). In the illustrated example, both bodies have different spectrum, that may appear different depending on the illumination type and light source.
For standardized color control it is necessary to choose D50 lighting for prints and D65 for industrial products, e.g. coatings, plastics, varnish etc. If you need to detect metamerism of the substrates, additional illuminants are needed.
With our color viewing booths you can choose between different dimensions and numbers of illuminants but always with illuminant D65 und A for detection of metamerism.
Source and further information:
DIN Deutsches Institut für Normung e.V. (2001): DIN EN ISO 3668:2001-12: Beschichtungsstoffe – Visueller Vergleich der Farbe von Beschichtungen (ISO 3668:1998); Deutsche Fassung EN ISO 3668:2001