Definition
CIE whiteness is an index that quantitatively evaluates the whiteness of the surface of objects based on the standard chromaticity system recommended by the International Council on Illumination (CIE). It is calculated through chromaticity coordinates and specific formulas, aiming to provide an objective and unified white evaluation method, widely used in materials science, textile, paper, plastics and other industries to evaluate the whiteness quality and consistency of products.
Principle
The calculation of CIE whiteness is based on the CIE standard colorimetric system, which is mainly based on the reflectance spectral data of objects under standard light sources. Its core principle is to measure the spectral reflectance of the sample in the visible light range, convert it into chromaticity parameters, and then substitute it into the formula recommended by CIE for calculation. Commonly used formulas include the CIE 1982 whiteness formula and the pale tone index formula, which take into account the degree to which the sample's position on the color quality map deviates from the ideal white.
The basic calculation formula is as follows: W = Y + 800 (x₀ - x) + 1700 (y₀ - y), where W represents the whiteness value, Y is the luminance factor, x and y are the color coordinates of the sample, and x₀, y₀ are the color coordinates of the fully diffuse reflector. This formula is effective within a defined range of color grades, ensuring consistency in results with visual perception.
Measurement method
CIE whiteness is usually measured using a spectrophotometer or colorimeter. The instrument measures the spectral reflectance of the sample under standard light sources (e.g., D65 light sources) and standard observer conditions, and automatically calculates the excellence coordinates and whiteness values. Instrument calibration is required before measurement, using a standard whiteboard as a reference. The sample should be flat and uniform, avoiding interference factors such as fluorescent brighteners, and the angle of the light source and observation conditions should be in line with CIE regulations when measuring to ensure data comparability.
Influencing factors
Sample surface properties such as texture, gloss, and uniformity affect the reflection of light, which can alter whiteness measurements. Colorants, fillers, or fluorescent substances in the material composition can cause color casts or brightness changes. Measurement conditions include the type of light source, viewing angle, and ambient light, which need to be strictly standardized to avoid deviation. The accuracy and calibration status of the instrument itself are also critical factors, and regular maintenance and calibration can help ensure measurement stability.
Application:
In the paper industry, CIE whiteness is used to evaluate the whiteness and hue of paper, guiding bleaching processes and quality control. The textile industry manages fabric bleaching effectiveness and dyeing uniformity through whiteness measurement. Plastics and coatings production relies on whiteness data to adjust formulations to ensure consistent product appearance. In addition, whiteness indicators are also commonly used in fields such as ceramics, building materials, and food packaging for quality monitoring and standard compliance verification.
Selection
When selecting a whiteness measurement instrument, consider measurement accuracy and repeatability to ensure compliance with industry standards such as ISO 11475. The instrument should support the light source and observation conditions recommended by CIE, and have spectral analysis capabilities to adapt to different materials. The user interface and software features need to facilitate data management and analysis. In addition, the stability and maintenance costs of the instrument should also be taken into account to adapt to the long-term use needs of the laboratory or production line.