Color Meter / Colour Meter

The measurement geometry describes the alignment between the emitting light source of the measuring device and the surface of the object to be measured as well as the alignment of the sensor to the reflecting surface of the object to be measured. The choice of the correct or incorrect measurement geometry can have a considerable effect on the measurement results and lead to interpretational errors during the information exchange between customers and / or suppliers. Since the measurement geometry cannot be changed or adjusted afterwards, clarity should be provided before the purchase. Known geometries are d / 8 and 45/0.

The d / 8 measurement geometry produces diffuse light, thereby the effect of the surface texture in terms of gloss and roughness is reduced. With this geometry, one can, so to say, look inside the color. Partially, measuring instruments with this geometry also have optical shines (SCI) (SCI) in order to allow the gloss effect influence the measurement or not. In contrast, the 45 / 0 measurement geometry produces a directed reflection which corresponds more to human perception. Therefore, it makes sense to use the 45 / 0 geometry, when the visual impression an object has on humans should be adjusted.

When selecting the accuracy requirements, attention should be paid to the reproducibility of the measurement results as well as the comparability of different measuring instruments of one series. Particularly in case of spectrometers, a spectral resolution of the measuring devices must also be taken into account.

An important point, which must be clarified before the purchase of a color measuring device, refers to the present reference values. Does it go about company's internal measurements, during which the process reliability and quality are to be checked based on specially defined color values? Or should the external requirements of customers or suppliers be taken into account? If external requirements are decisive, a preliminary clarification between the parties, concerning which measuring instruments are to be used, is required. It is particularly important to achieve an agreement about measurement parameters (color space, measurement geometry, measuring aperture, light type, SCI, SCE, Spin, Spex); otherwise the comparability of the measurement values is not possible. Ideally, both parties use identical measuring devices from one manufacturer.

Many comparative measurements take the color values from standard color systems or color catalogs into account. Known color catalogs are e.g. RAL, NCS, DIN or Pantone. Based on these catalogs, visual inspections can be carried out during the production process and quality control. The visual comparison of color cards with printing inks, coloring or colored coatings is, however, faulty, since it is often impossible to check it objectively under the same conditions. Reproducibility and objectivity can be provided by the color meter, since under defined conditions digitally stored color catalogs can be matched with the customer color patterns.

In addition to color cards, often also color spaces like the CIELab or RGB color space are used to determine colors. The color spaces are geometrically defined, three-dimensional bodies, in which each color is characterized by 3 coordinates in the X, Y and Z directions. By specifying the spatial coordinates of the corresponding color space, the colors can be exactly determined and the color spacing can be precisely estimated. Since color spaces, in contrast to color catalogs, can represent all perceptible colors and are used not only in a few industries and, therefore, are universally applicable, the use of color spaces is often more comparable and independent.

The use of different light types can change the perception of color impressions. The CIE has therefore established standard illuminants with a defined spectral emission in order to create comparability. The choice of the applied type of light had to be oriented to the later application of the product. The widely spread standard light type is D65. D65 simulates the daylight with UV components at a color temperature of about 6500 Kelvin. The standard light type C also stands for daylight, but without UV components at a color temperature of about 6770 Kelvin. The light type F11 or TL84 is also referred to as department store light at 4000 Kelvin and is suitable when the products are kept under artificial light. In addition to these light types, there are many others from narrow- to broadband standard light types.

Depending on the application, a suitable design is also to be selected in the sense of ergonomics. In some devices, the display is placed on the top, while in the other color meters the data is read from the front side and the sensor system is internally installed in a housing. Besides, there are also measuring instruments with external sensors. In addition, some measuring instruments have built-in cameras to assist in the positioning of the measuring device on the object to be measured. Particularly for small objects and small apertures, this function helps to choose the correct positioning of the device, and thus, “hit” the measuring point.

Can smooth, flat and solid surfaces be measured? Does it go about liquids or should the color of fine powders be determined? Are they coarse granules or viscous pastes? There are solutions for all applications. If the surfaces are not smooth, hardened, then mostly special devices with partially transparent cuvettes are required. In these cuvettes, the materials of different consistencies can be measured and tested.