Ed #12 Standards
In addition to weight, paper is graded by brightness, a measure of the amount of light reflected by the paper. The brightness of the paper is determined by how the pulp is bleached, the mixture of dyes and pigments added to the pulp in the papermaking process and if it is a coated paper by the dyes, pigments and brightening agents used in the paper’s coating.
Brightness is measured in several different ways: In the United States and Canada, brightness is most often measured by the TAPPI (Technical Association of the Pulp and Paper Industry) scale, which compares the amount of light reflected by the paper surface to the amount of the same wavelength of light reflected by magnesium oxide, one of the brightest commonly available materials. The light that is used in the test is filtered at 457 nanometers, which falls in the blue region of the visible light spectrum. The brightness of most European and Asian papers is measured using either ISO or D65 standards, which produce different brightness readings.
Brightness is important because it determines the intensity of the color we see. Higher quality white coated papers typically have TAPPI brightness ratings in the 80s and 90s, with the numbers representing the percentage of light in the 457-nanometer wavelength that strikes the surface of the paper and is reflected back to the eye. While you might think that brighter paper is always better, that may not be the case. Because brightness is measured at the blue end of the visible light spectrum, a blue-tinted paper will have a higher brightness rating than a balanced white sheet. If a paper is too blue, however, it can affect the accuracy of the color that is printed—warm colors can develop a cool tint and yellows can become pale and weak. So in making paper buying decisions, you first should make sure that the papers you’re considering are measured by the same brightness standards. Then, you should look beyond the numbers and compare samples.