The percentage of white content or whiteness is the measure of white on the surface of a substance. The standard for whiteness is magnesium oxide set at 100%, followed by standard reflectance at the same mark. Estimation of three different values is done using three light sources, where the average value represents the whiteness of the three colors. Reflectivity and whiteness share a direct relationship; high reflectivity equates to a high degree of whiteness. The unit of whiteness “%” should be used, which is synonymous with the degree. For example, the witness of newsprint is 55 to 70 degrees can also be presented as 55% to 70%.
A surface object can be considered white if the surface reflectance of an object to all wavelengths is above 80% in the visible spectrum. The color space range for white is relatively narrow, and just like other colors, white can be expressed by three-dimensional qualities such as tight reflectance, purity, and dominant wavelength. Still, most people follow the conventional method to quantitatively assess the whiteness of objections using different whiteness as per one-dimensional whiteness. The reference standard is ideal whiteness (i.e., high-purity barium sulfate with a 100% whiteness value). It’s important to use the established standards when determining whiteness, whether by an instrument or visualization. Therefore, the term “whiteness” refers to the difference between the ideal white and the actual white.
The spectral reflectance curve presents white fabric as a smooth curve void of any wave peaks in the visible light band. Bleaching enhances the reflectivity of the white fabric, which provides an upward shift to the curve. However, the curve is bound to fall from the 510–700nm segment if the fabric is bleached and blue-whitened. As a result, reflectivity is enhanced in the 400–519nm segment. Fluorescent white treatment also increases the curve to a 400–550nm section. Therefore, whitening aims to increase the spectrum’s reflectivity at the blue end.
As discussed previously, whiteness represents the standard of whiteness of an object. Therefore, the higher the whiteness value, the higher the degree of whiteness. An integrating sphere is an essential part of a whiteness meter that determines the absolute spectral diffuse reflectance and measures whiteness. A whiteness meter can assess the whiteness of multiple objects, including cardboard, paper, chemical fiber pulp, cotton, pulp, textiles, plastics, starch, salt, ceramics, white cement, plastics, talcum powder, etc. Furthermore, it can be classified as:
- Intelligent Whiteness Meter
- Digital Whiteness Meter
Principle of Intelligent Whiteness Meter:
The integrating sphere is used to measure the absolute spectral diffuse reflectance. The optical principle is based on the blue light directed by the semiconductor light source entering the integrating sphere. The surface sample reflects the spectrum received by the silicon photon cell and reorganized into an electrical single after moving across the condenser, diaphragm, and color filter set. Once the single-chip microcomputer completes the processing mechanism, working whiteboard calibration, automatic zero calibration, and sample testing are obtained.
Uses of whiteness meter:
Salt plays various essential roles, such as a condiment in food and the main source of the daily salt requirement. Additionally, sensory indicators are just as important as chemical indicators when determining the quality of salt products. Various physical and chemical factors can influence color. For example, a salt containing copper, iron, water, insoluble matter, or ferric ferricyanide can greatly alter the whiteness value.
The difference in the whiteness of crystalline salt and crushed dry salt is mainly because physical properties can influence whiteness. The reason behind the difference is based on reflectance. Crystalline salt absorbs light easily, reducing the light reflectance and decreasing the whiteness value. However, reflectance increases for crushed and dried salt, so whiteness increases.
The whiteness meter can evaluate the whiteness of salt more efficiently. It is also primarily used in printing, textile printing, chemical industry, food, salt making, and several other industries to determine the whiteness of an object.
Whiteness detection of paper packaging
Paper whiteness or brightness of a paper is the capacity of the paper to reflect after being illuminated by light. High values of whiteness are linked with accurate expression of characteristic ink color. The reason is the reflection of color light produced by the subtractive color of the transparent ink layer. Therefore, paper with high whiteness values produces more eye-pleasing printed products due to the light reflection of all colors. In contrast, those with low whiteness value are not as pleasing to the eye because it only absorbs a fraction of color light. A whiteness meter can help determine the whiteness of paper to enhance the production quality.
What is the best way to utilise a whiteness metre?
Approximately 10 or more samples of 150x755mm are taken that are treated with appropriate temperature and humidity conditions. (Temperature 23 ± 2 ℃, relative humidity 45% — 55%). Switch on the reflection photometer and warm-up for 10 minutes.
Place the black cylinder on the sample holder by pressing the slide cylinder pressure plate of the sample holder. Allow the cylinder to reach up to the measurement port. Once the value displayed on the digital screen is stable, adjust the zero adjustments now. The display should now be on 00.0
- Worksheet whiteness value
The black tube should be placed on the working standard whiteboard after removal. Once the display value stabilizes itself, regulate the calibration knob to align the displayed value with the whiteness value on the standard plate. Now, remove the working standard whiteboard and place the reference standard whiteboard instead. Record the whiteness value. Later, the value is calibrated as the nominal value and carefully placed in a desiccator filled with silica gel.
Before sample measurement, a black tube and a reference standard white place should be used.
- Measurement of whiteness
In the case of a non-fluorescent paper, the sample to be tested is set on the sample holder as the instrument is pre-adjusted. The whiteness value is presented automatically once the displayed value achieves stability.
How to calibrate the whiteness meter?
When the whiteness of the working board does not correlate with the standard (Orignal whiteboard) of the whiteness meter, make necessary adjustments in the position and amount:
Select Position: Push the select position button to brighten one of the three displays. Push the button again to shift the bright position to the left.
Liter Number: Similarly, push the number of liters to see a brighter digit. Push it repeatedly until the desired value displayed is compatible with the value on the back of the whiteboard. Place the board in the sample port, push the calibration button and wait for three seconds for the whiteness value to be displayed.
What separates a colorimeter and whiteness meter?
Evaluation of color difference can be easily completed with the help of a colorimeter. It detects the L, a, and b values and the color difference value. However, the whiteness meter mainly focuses on calculating the blue light whiteness of the surface of the object.
The colorimeter is an instrument specially used to detect the color difference of the product or to assist the color matching. It can measure the L, a, and b values and the color difference value, but it is primarily used for measuring the color difference value. Both the instruments are based on optical detection but are fairly different in their approach.
What is the measurement range of the whiteness meter?
The range of a whiteness meter includes paint, diatomite, bentonite, white cement, colored cement, titanium dioxide, washing powder, etc. Calcium, kaolin, solid samples with certain planes (paper, cloth, ceramics), and wollastonite are also included.
However, it’s primarily for measuring the whiteness of objects with a flat surface. It can acquire the whiteness value consistent with the visual sensitivity. Furthermore, the fluorescent whitening agent treated objects can be measured for whiteness value after the fluorescent brightening is reflected.
Last but not least, it can be used to determine the whiteness of textile printing and dyeing, paint and coatings, chemical construction materials, paper and cardboard, plastic products, white cement, ceramics, enamel, talc, starch, flour, salt, detergent, cosmetics, and other items.
The difference between blue light whiteness, Henry whiteness, and Gantz whiteness
As discussed previously, white can be displayed in three-dimensional quantities, but people prefer revelation based on the one-dimensional whiteness. It’s established that “whiteness” determines the degree of whiteness of an object. Therefore, exposure of a white object to sunlight shifts it towards the yellow gradient. Now, “yellowness” describes the color of the object. Whiteness measurement is a necessity in various industries, and the following indicators are used:
- Blue light whiteness: The whiteness is represented using the single-band whiteness formula, which uses the reflectance of a spectral region. ISO brightness is the measurement of blue light diffuse reflectance factor in the short-band region.
- Henry Whiteness:The Henry color lab space is utilized as the approach of whiteness is related to the color difference.
- Gantz Whiteness: The addition of a weighting factor during the determination of whiteness was proposed by Gantz. Therefore, known as the Gantz Whiteness.