Overview
In the field of ink manufacturing and application, accurate color evaluation and consistency control are core quality links. As an intuitive and widely used evaluation method, the reliability of visual colorimetric method is highly dependent on the lighting and observation conditions during observation. The standardized visual coloribox, which simulates and controls a specific optical environment, provides a stable and repeatable observation platform for evaluators, thereby minimizing visual biases caused by factors such as ambient light, light source characteristics, and viewing angles, and ensuring the objectivity and comparability of color evaluation results.
Technical requirements:
The design and use of standardized cuvettes must strictly follow relevant technical standards, and the core of which lies in the specification of light source, background and observation geometric conditions.
The spectral power distribution of the light source is the decisive factor. The International Illumination Commission (CIE) recommends the use of standard light sources to define colorimetric conditions. For example, the D65 light source represents the average northern daylight and is a common standard light source for evaluating the color of materials. Its relative spectral power distribution S(λ) is the basis for color calculations. In the colorbox, the correlated color temperature and color rendering index of the analog light source should be as close as possible to the standard requirements, usually the correlated color temperature deviation should be controlled within ±200 K, and the general color rendering index Ra should be greater than 90. The illuminance uniformity of the light source is also critical, and the coefficient of illuminance variation in the work area should be less than 15% to ensure that the sample surface is evenly illuminated.
The background color of the observed environment must be neutral. Neutral gray-matte materials with a Munsellian brightness value of about 6 to 8 are usually used as the background of the inner wall, and their color coordinates should be close to the neutral point under the CIE standard illuminator, for example, at D65 (x=0.3127, y=0.3290). This effectively avoids the contrasting or assimilation effect of background color on the observer's color perception.
Observation geometric conditions need to be standardized. The two common conditions are 0°/45° (illumination vertical incidence/45° direction observation) and 45°/0°. The mathematical relationship can be expressed as follows: the angle between the observation direction and the normal of the sample is strictly 45°±2°, or the illumination direction is equal to this angle. This fixed geometry ensures that the surface texture aligns with the impact of gloss on color perception.
Influencing factor control
After establishing a standardized environment, standardized operating procedures are another key to ensure the effectiveness of evaluation results. Before evaluation, the light source needs to be warmed to a steady state, usually more than 15 minutes. Sample placement should ensure that it completely covers the viewing hole and that the area to be measured is centered in the uniformly illuminated area. The observer is subject to color vision examination and visual acclimatization prior to assessment, acclimatizing for no less than 60 seconds against a cuvette neutral gray background.
Interference in the environment must be effectively isolated. The cuvette should have good shading to prevent external light intrusion. The inner wall of the box needs to be cleaned regularly to avoid dust accumulation and change the reflection properties. In addition, the characteristics of the sample itself, such as opacity and gloss, should be noted in the evaluation report, as they can directly affect the visual perception results.
Technical parameters
| Core parameters | Typical technical requirements |
| Standard light type | D65, D50, CWF, TL84, UV等 |
| Correlation color temperature tolerance | ±200 K (relative to nominal) |
| General color rendering index Ra | > 90 |
| Illuminance uniformity | Coefficient of variation in the working area < 15% |
| Background color brightness | Munsell brightness value N6 ~ N8 |
| Background color gloss | Matte (gloss unit < 10) |
| Observe geometric conditions | 0°/45° or 45°/0° |
| Ambient light isolation | No external light leakage |
Conclusion
The construction of a standardized environment for visual color cuvettes is the cornerstone of quality control for visual evaluation of ink colors. By strictly regulating the spectral and spatial characteristics of light sources, neutralizing the background and the geometric conditions of observation, supplemented by standardized operation procedures, the consistency and reliability of color judgment can be significantly improved between different times, different places, and different operators. This provides crucial technical support for raw material acceptance, production process control, and final product inspection in the ink industry, and promotes the accuracy of color information transmission in the supply chain.
References
International Illumination Commission. CIE 015:2018 Colorimetry.
American Society for Testing and Materials. ASTM D1729 Standard Practice for Visual Evaluation of Opaque Materials.
International Organization for Standardization. ISO 3664:2009 Imaging techniques and photography - Observation conditions.
National Printing Standardization Technical Committee. GB/T 7705-2008 Lithography decoration prints.