Bei einem Farbmessgerät bezieht sich Geometrie auf die Art und Weise, wie Licht auf die Oberfläche eines Objekts trifft und reflektiert wird, sowie auf den Winkel, unter dem die Farbmessung erfolgt. Die Wahl der Geometrie beeinflusst die genaue Messung der Farbe, da verschiedene Oberflächen unterschiedliche Reflexionseigenschaften haben.
45°/0°, 0°/45°
In a 45°/0° geometry device, the sample is illuminated at a 45° angle, and the reflected light is collected by the receiver at 0°. The illumination is typically circular around the sample at 45°, referred to as “omnidirectional illumination.” In a 0°/45° geometry device, the sample is illuminated at a 0° angle, and the reflected light is collected at 45°. Usually, multiple receivers are arranged in a circular pattern, known as “omni-observation.” Both geometries are referred to as reciprocal because the results, according to optical laws, are identical. Devices with 45°/0° or 0°/45° geometry always measure under gloss exclusion. They measure the visual impression of the sample and best reflect the color perception of the human eye. These geometries are typically used when the overall appearance of a specific color is to be measured. A shiny sample, when viewed, will appear darker and more saturated than a matte sample, even if both samples are identically pigmented.
Diffuse/8°
What is meant by the term “diffuse/8°”? In a device with a diffuse/8° geometry, the sample is illuminated diffusely, meaning light is scattered from all directions. The observer receives the reflected light from a position that is 8° to the normal (perpendicular) to the sample surface. The diffuse/8° geometry is also known as “sphere geometry” because a sphere with a white interior coating is used for light projection. Multiple reflections inside the sphere lead to color mixing. The 8° deviation of the observer from the sample surface allows for reflection measurement with or without gloss inclusion in some HunterLab devices. In the gloss-inclusion measurement mode (RSIN), the total reflection, meaning both diffuse and specular reflection (direct reflection of the light beam, mirror-like reflection, or gloss), is measured. In the gloss-exclusion mode, only the diffuse reflection is measured. The gloss component is eliminated by opening part of the sphere from which light is normally directly reflected from the sample to the receiver.