- Brightness measures the light reflectance in the blue region of the visible light spectrum.
- Optical brightening agents (OBAs) increase the reflectance of blue light.
- To increase brightness measurement:
- Increase OBA
- Increase UV energy in light source
Brightness can be measured by a variety of methods. On any given paper, the brightness number given by each of these methods will be different. Papers may be sold based on TAPPI, ISO or D65 Brightness. Enterprise Group papers are sold based on TAPPI Brightness. Many competitive products are sold using any one of these brightness scales and it is important to understand what measurement they are using when comparing to Enterprise Group products.
TAPPI Brightness - the North American standard that quantifies the brightness of paper as it would be perceived in an environment that is illuminated with a mixture of cool-white fluorescence and some filtered daylight. The ultra-violet light component of TAPPI brightness is the lowest of any standard. In addition, light hits the sample from only one particular angle (ISO and D65 brightness measurements are diffuse,meaning light hits the sample from all angles). Therefore, TAPPI Brightness will provide the lowest number of any of the three scales. TAPPI Brightness numbers will rarely exceed 100%.
ISO Brightness - the European standard that quantifies the brightness of paper as it would be perceived in an environment that is illuminated with a mixture of cool-white fluorescence and some unfiltered daylight. The fluorescence present in a paper sample, which can provide a significant contribution to brightness, will be stimulated more using the ISO standard versus TAPPI. Therefore, the ISO standard will always yield a higher brightness versus TAPPI for the same paper. ISO Brightness numbers can exceed 100%, but not by too much.
D65 Brightness - a measurement that is based on perceived brightness for paper viewed in north sky daylight. Because outdoor light has the maximum amount of ultraviolet light available to interact with the fluorescent component of brightness, it will produce brightness numbers that are significantly elevated and could easily exceed 100%. D65 brightness numbers will always be much higher than TAPPI or ISO for the same paper because of the highly magnified fluorescence component.