What is Whiteness ? What is the Whiteness index?

Whiteness is the ability of a material to reflect light and how white it appears visually. In general, white materials reflect light evenly across the entire visible spectrum, appearing bright and without color cast. Whiteness is determined not only by the brightness of a material, but also by its hue (color cast). Visually, people prefer "bluish-white" materials to yellowish or grayish white. Therefore, Whiteness can be understood as a subjective visual perception that is affected by factors such as the light source, the observer's perspective, and the properties of the material.

Whiteness Index is an optical index used to quantitatively evaluate the "Whiteness" of a material. It is based on the characteristics of the material's reflected light, and uses a set of standardized calculation formulas to measure "how white" an object looks, and assign it a numerical value. Whiteness Index is usually used to evaluate the visual Whiteness of products such as paper, textiles, coatings, and plastics, and is of great significance to material quality control and visual effect evaluation.

The calculation of the Whiteness index depends on spectral measurement data, and different Whiteness index standards use different calculation formulas and conditions, for example:

· ASTM E313 , CIE/ISO , AATCC and Hunter are all different Whiteness index standards, each designed according to specific application scenarios to meet the needs of different materials and industries.

· The calculation of the Whiteness index generally takes into account the material's reflection of blue and yellow light, and may even add the effect of fluorescent brighteners to improve the visual Whiteness effect.

Common standards for Whiteness

ASTM E313 Whiteness Index

· Definition : ASTM E313 Whiteness Index is a standard developed by the American Society for Testing and Materials (ASTM) and is primarily used to measure the Whiteness of materials such as paper, plastics and textiles, especially those that contain fluorescent whitening agents.

· Measurement method : ASTM E313 Whiteness index calculates Whiteness based on the difference in reflection of blue light and yellow components. Its calculation formula is defined according to the reflectivity of a specific wavelength range and is suitable for Whiteness evaluation of bluish-white materials.

· Application scenarios : This standard is widely used in industries such as paper, plastics and textiles. It is particularly suitable for detecting materials with fluorescent brighteners and can reflect the visual Whiteness effect of the material.

AATCC Whiteness Index

· Definition: AATCC (American Association of Textile Chemists and Colorists) Whiteness Index is used to measure the Whiteness of textiles, especially for bleached and whitened products in the textile industry.

· Measurement method: AATCC Whiteness Index is based on the measurement of blue light reflectance, similar to ASTM E313, but this method is specifically for textiles. AATCC Whiteness Index can also reflect the impact of fluorescent brighteners, especially for the evaluation of the effect of bleaching or whitening treatment in textiles.

· Application scenarios: This index is widely used in the bleaching, dyeing and printing processes in the textile industry to ensure that products meet specific Whiteness standards. For textiles that require Whiteness enhancement, the AATCC Whiteness Index is a commonly used measurement method.

Hunter Whiteness Index

· Definition : Hunter Whiteness Index is a Whiteness measurement method developed by HunterLab, which calculates Whiteness based on L, a, b values in Lab color space. It can be used to measure the Whiteness of a variety of materials, including paper, plastics, coatings and building materials.

· Measurement method : Hunter Whiteness Index uses the L value (brightness) and b value (chromaticity in the blue-yellow direction) in the CIE Lab color space to calculate Whiteness. Specifically, Hunter Whiteness Index is usually calculated using the formula "WI = L – 3b", which more directly reflects the "blue-Whiteness" effect of the material.

· Application scenarios : Hunter Whiteness index is used to evaluate visual Whiteness and is widely used in industries such as plastics, paints, coatings, paper and ceramics. It is widely used in industry because its calculation method is relatively simple and is applicable to a variety of materials.

CIE Whiteness Index (ISO 11475/11476)

· Definition : CIE Whiteness is a Whiteness standard jointly developed by the International Commission on Illumination (CIE) and ISO. CIE Whiteness standard ISO 11475 is applicable to Whiteness measurement under simulated daylight (D65 light source) conditions, and ISO 11476 is applicable to Whiteness measurement under C light source conditions. This standard defines the Whiteness perception of materials under different light sources.

· Formula: WCIE = Y + 800(xn - x) + 1700(yn - y)

where Y is the luminance of the sample (Y tristimulus value), x and y are the chromaticity coordinates of the sample, and xn, yn are the chromaticity coordinates of a perfect diffuser for the CIE 1964 standard colorimetric observer.

· Measurement method :

o ISO 11475 (D65 Daylight Whiteness) : Measures the reflectance spectrum of a material under a D65 standard light source (simulated daylight) to reflect its Whiteness under daylight conditions.

o ISO 11476 (Whiteness under illuminant C): This method is used to measure the Whiteness of a material under different illuminants.

· Application scenarios : CIE Whiteness is widely used to measure the Whiteness of various materials, including textiles, paper, plastics, and building materials. Since this standard is more consistent with the human eye's perception of Whiteness under natural light, it is particularly suitable for products that require strict Whiteness control.

Ganz Whiteness Index

· Definition : Ganz Whiteness is a Whiteness measurement standard proposed by Swiss scientist Eugen Ganz. It is used to evaluate the Whiteness of materials such as paper, textiles, and plastics. The Ganz Whiteness standard is particularly suitable for materials that do not contain fluorescent whitening agents and aims to provide a Whiteness evaluation method that conforms to human eye perception.

· Measurement method :

o Ganz Whiteness is calculated based on the spectral reflectance of the material in the visible spectrum range of 400 nm to 700 nm. The formula is:

W=R+3(B−Y)

Where W is the Gantz Whiteness value, R represents the brightness reflectance value of the material, and B and Y are the blue and yellow reflectance values respectively. Through this calculation method, Gantz Whiteness can highlight the blue component and suppress the yellow component, thus producing a visual "blue and white" effect.

· Application scenarios : Ganz Whiteness is widely used in the paper, textile and plastic industries, and is suitable for materials without fluorescent whitening agents. Since this method conforms to the natural perception of Whiteness by the human eye, Ganz Whiteness is used in the paper, textile and plastic fields to ensure the Whiteness of products under natural light, and is particularly suitable for quality control of materials with high Whiteness and no fluorescent whitening agents.

How to measure Whiteness? Whiteness test methods

Whiteness is usually measured using instruments such as spectrophotometers or colorimeters, which calculate Whiteness by measuring the reflectivity of a material to a specific light source. Whiteness measurement methods vary according to different industry standards. Common Whiteness measurement methods include:

1. Reflectance method : Use a spectrophotometer or integrating sphere device to measure the reflectance of a material at a specific wavelength (such as 457 nm blue light). This method is commonly used in industries such as paper, plastics and textiles to evaluate the visual Whiteness of materials.

2. Integrating sphere method : By placing the sample inside an integrating sphere, the reflected light intensity of the material under a D65 or C light source is measured to simulate the Whiteness effect under daylight conditions. This method is particularly suitable for materials containing fluorescent whitening agents.

3. Fluorescence Whiteness method : For materials containing fluorescent whitening agents, the Whiteness enhancement effect of the material under ultraviolet light is measured. The fluorescence Whiteness method is applicable to the paper, textile and plastic industries to help evaluate the whitening effect.

4. CIE Whiteness Index Calculation : According to ISO 11475 and ISO 11476 standards, the Whiteness index is calculated using the CIE formula, which is applicable to a variety of materials and is more consistent with the human eye's perception of Whiteness.

3nh Whiteness measurement solution

Whiteness measurement solutions mainly based on its colorimeter and spectrophotometer products , which have accurate colorimetric measurement capabilities and can be used for Whiteness measurement of different materials.

Colorimeter :

1. 3nh's colorimeter can measure the chromaticity coordinates of materials under standard light sources (such as D65) and calculate the Whiteness index based on the measured data.

2. The colorimeter is easy to operate and suitable for rapid Whiteness detection of paper, plastic and textiles. It is applicable to Whiteness measurement needs in production lines or laboratories.

Spectrophotometer :

1. 3nh's spectrophotometer has higher accuracy and sensitivity, and can provide full spectrum data. The spectrophotometer can measure the reflectance of materials at different wavelengths to calculate the Whiteness index under different standards (such as TAPPI T452, ISO 2470, CIE Whiteness, etc.).

2. Suitable for industries that require accurate Whiteness measurement, such as paper, textiles, plastics, etc., spectrophotometers can meet the needs of quality control and scientific research testing.