There are so many testing methods of whiteness, and the reliability and applicable range are varied, especially as the increasing use of the fluorescent whitening agent in recent years, making the determination of whiteness become much more complicated. Nowadays, the determination of whiteness can be divided as two kinds generally: the first one is to use the spectrophotometer to determine the reflectance of each wavelength. The L value, a value and b value are obtained by computer calculation, and then the whiteness is obtained by the whiteness calculation formula. At present, there are a lot of whiteness calculation formulas, but they are all have weakness, proving that it is hard to find a formula that is corresponded to the fact. Taking ZBD whiteness calculation as an example: Determination of the specific wavelength light through the filter that transmitted wavelength less than 500nm is irradiated to the sample light except for the blue light, and purple light, so that whiteness measurement can be carried out with samples of fluorescent whitening agents. In the determination, the instrument is adjusted with a standard white plate, and then the relative whiteness of the sample is determined.   

1. Instrument. XBD  whiteness calculation.

2. Operating steps. To cut the semi-cloth products with no optical brightener for 12cm refined * 24cm, and fold into 5cm * 5cm 8 layers (thin fabric is 18cm * 24cm, 5cm * 5cm folded into 12 layers). And then to determine whiteness in whiteness meter, which requires each specimen shall keep the warp and weft consistent. In this case it should be measured 3 times in different parts, and eventually to take the average value.

3. Illustrations
◎ Other instruments which can determine or can calculate after determination are favorable to be applied. Even though the data gained may not consistent, using the same instrument to determine the data can still illustrate the situation about whiteness. The date of whiteness given in the report should be marked the type of the instrument.
◎ The layers folded of textile should be the same.