The model treats light inside paper as two diffuse streams, one moving down and one moving up, each losing intensity to absorption and redirected by scattering. From it, R-infinity depends only on the ratio k/s, through k/s = (1 - R-infinity) squared divided by (2 R-infinity), while R0 and grammage give s itself. Papermakers use it to predict how much filler, dye or grammage change is needed to hit a brightness and opacity target.
Run the Kubelka-Munk numbers before the trial; if s doesn't move, more PCC won't buy them the opacity.
The model assumes a uniform, matte, non-fluorescent sheet, so values on glossy, coated or brightened papers are approximations.
Also heard as
- K-M theory
- KM theory
Related terms
Light-scattering coefficient
Per-grammage measure of how strongly a paper redirects light, written s and given in square meters per kilogram.
Light-absorption coefficient
Per-grammage measure of how much light a paper absorbs, written k and given in square meters per kilogram.
R-infinity
Reflectance factor of a pad so thick that adding more sheets no longer changes the reading.
R0
Reflectance factor of one sheet measured over a black cavity, the starting point for every opacity calculation.
PC number
Post color number: a Kubelka-Munk measure of how much a pulp yellows during an aging test.