Honey yellow, raspberry red, sapphire blue, or moss green are very attractive, descriptive color names. However, are you sure everyone represents the same color? Usually not. How do you clearly describe a color and guarantee the same color over time?
Our color perception is determined by our personal "taste", which is affected by our mood, gender, age, and the light source used, be it bright or dark, neutral or colorful and our lack of accurate memory and memory Defects convey a specific color.
Standardized viewing conditions
For a controlled visual and instrumental assessment, the light source, surrounding environment and observer should be defined. Colors may match under one light source (sunlight) but not under another (fluorescent light). This effect is known as metamerism and is a key quality requirement for multicomponent products. Therefore, a match needs to be verified using the kind of light that might be found where the product is sold or used. Commonly used light sources are standardized at CIE (International Commission DE L'. clairage).
ISO and ASTM standards define ambient as the field of view around the sample as well as the peripheral field of view (when the observer looks away from the sample, such as the interior surfaces of a lighting booth). It shall be of Munsell notation N5-N7 in color and shall have a 60° gloss not greater than 15 GU.
Observers for visual assessments should have normal color vision and be trained to observe and classify colors. A vision test is recommended to periodically check the observer's color vision as it changes over time (see ASTM E1499 guidelines). Observers for instrumental color controls were normalized using two different fields of view: a 2° standard observer and a 10° standard observer. Today, the 10° observer function is mainly used, since the eyes can be integrated over a larger area.
Standardized measurement parameters
For instrumental color measurement, the optical properties of the product need to be measured. A Spectrophotometer measures the amount of light reflected by objects at different wavelengths in the visible range (400 - 700 nanometers). Reflectance curves display spectral data and act as a "fingerprint" of an object's color.
Internationally standardized color systems, such as the widely used CIELab system, describe colors in three data colors that combine the luminance, hue, and chrominance components of a standardized illuminant, a standardized observer, and spectral reflectance data.
Establish tolerances on each color component or on the total color difference ΔE*.
Over the years, new color systems and equations (ΔECMC–ΔE94–ΔE99–ΔE2000) have been developed based on visual comparison studies of pure colors to improve visual correlation, thus exhibiting elliptic tolerance behavior.
standardized instrument geometry
International standards define the geometrical conditions for Spectrophotometer s:
45/0 – control color
For final solid-color QC, 45° circumferential illumination is defined to achieve reproducible results on unstructured and structured surfaces.
d/8 – controls the hue of the color
Diffuse lighting is required if you want to control color unaffected by surface sheen or texture.
