Defining Brightness and Whiteness in Paper

I am often asked about how paper brightness is determined and what the brightness value means. USDA Forest Service recently released an explanation.
To date, the industry used two methods - both yielding different results -
GE - measured the percent of total light reflectance.
ISO - defined the percentage of blue light reflected from the paper's surface.
FYI. The GE figure was always greater than the ISO value - sometimes even greater than 100%
Both measurements only provided a brightness value - with no attention to whiteness.
USDA has mandated the paper industry to use a uniform measurement - called CIE - this will be an international
agreement for all paper manufacturers. This scale measures whiteness versus the narrow color band of blue white and brightness.

Brightness may or may not add much value to the 'useful' properties of the paper but it is the most important selling feature. It is a bragging right every paper manufacturer want to have that the mill produce most bright paper.
Brightness is defined as the percentage reflectance of blue light only at a wavelength of 457 nm. Whiteness refers to the extent that paper diffusely reflects light of all wavelengths throughout the visible spectrum. Whiteness is an appearance term. Color is an aesthetic value. Color may appear different when viewed under a different light source. Brightness is arbitrarily defined, but carefully standardized, blue reflectance that is used throughout the pulp and paper industry for the control of mill processes and in certain types of research and development programs. Brightness is not whiteness. However, the brightness values of the pulps and pigments going into the paper provide an excellent measure of the maximum whiteness that can be achieved with proper tinting.
As outlined above brightness is measured with two different standards - TAPPI/GE and ISO. Though there is no direct correlation, ISO brightness of a sample is usually lower by 1-1.5 units over GE brightness. The standards are as per Tappi T 452.
Color is related to perception and therefore measured or specified in terms of color space. A commonly used system is the CIE L,a,b system. This is based on the idea of color opposites.
L - measure of luminance and varies from 100 for perfect white to 0 for perfect black.
a - redness to greenness.
b - yellowness to blueness.
Whiteness is the extent to which paper diffusely reflects light of all wavelengths throughout the visible spectrum i.e. the magnitude & uniformity of spectral reflectance measured as the percent light reflectance for the whole wavelength range. The procedural standards for the measurement of whiteness are explained in ISO 11475.
the measurement of whiteness are explained in ISO 11475.