The international brightness method (ISO 2470-1) lights the specimen diffusely through an integrating sphere, views it at 0 degrees and reports R457 on an opaque pad. The instrument's UV content is adjusted with fluorescent reference standards so that optical brighteners respond as they would under CIE illuminant C. Most market pulp outside North America, and much of it inside, is bought and sold on ISO brightness.
Contract says 89 ISO brightness minimum and the last three bales came in at 88.4, so the pulp mill is getting a call.
When a pulp buyer and seller disagree by half a point, compare UV calibration dates and reference standard lots before arguing about the pulp.
Also heard as
- ISO 2470 brightness
- diffuse brightness
- R457 C
Do not mix it up with
- D65 brightness: D65 brightness uses the same geometry but more UV, so sheets with optical brightener read several points higher than their ISO brightness.
Related terms
Brightness
The blue-light reflectance of pulp or paper, read at an effective wavelength of 457 nm and reported as a percentage.
d/0 geometry
Measurement setup with diffuse illumination of the sample and viewing perpendicular to its surface.
Illuminant C
Standard CIE light distribution approximating average daylight, with relatively little ultraviolet.
TAPPI brightness
North American directional brightness measured with 45/0 geometry at 457 nm, widely called GE brightness.
UV calibration
Setting an instrument's ultraviolet content so fluorescent samples read as they would under the specified illuminant.