Brightness is the most extensively used optical property of pulp, paper, and paperboard. The measurement of brightness (blue reflectance) was originally devised as a means of quantitatively assessing the effectiveness of pulp bleaching. A specific spectral response has been defined and rigorously maintained, providing long–term stability of brightness values to the industry.

The accurate determination of brightness is of vital importance in the buy-sell relationship between the paper producer and consumer. High brightness is an indication of high-quality paper, resulting in a price structure where price is relatively proportional to the brightness level. Paper producers are required to employ additional bleaching or the addition of costly optical brighteners in order to obtain high-brightness paper. The high cost of such brightening materials mandates adherence to close production tolerances for the brightness of the end product.

1.1 This test method determines the brightness of white, near-white, and naturally colored pulp, paper, and paperboard. Brightness is a commonly used industry term for the numerical value of the reflectance factor of a sample, with respect to blue light of specific spectral and geometric characteristics. This test method requires an instrument employing 45 illumination and 0 viewing geometry, with the illuminating and viewing beams adjusted so that translucent materials are evaluated on an arbitrary but specific scale (1-4).

1.2 This test method is applicable to all naturally-colored pulps, and papers and board made from pulps. The measurement is not suitable for paper and paperboard containing added coloring matter (such as yellow or green dyestuff) which appreciably absorbs light in that part of the spectrum extending from about 400 to 500 nm. Colored papers must be measured spectrophotometrically or colorimetrically in order to obtain meaningful results (TAPPI T442, T524, and T527). This test method is, however, suitable for pulps or papers which contain optical (fluorescent) brightening agents.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.