A single-number rating of how much blue light a pulp or paper reflects, measured with a filter or weighting function centered on 457 nm and compared with a perfect reflecting diffuser. The blue band was chosen because yellowing from lignin and other chromophores shows up first as lost blue reflectance, so brightness tracks bleaching directly. It is not a color measurement: two sheets with equal brightness can look clearly different in hue and whiteness.
Pulp mill is shipping us 88 brightness instead of 90, so the machine will need more OBA to hold the spec.
Always ask which brightness: ISO and TAPPI readings on the same sheet usually differ, and brightened papers swing further depending on the UV in the light source.
Also heard as
- blue reflectance
Do not mix it up with
- Whiteness: Whiteness rates the visual impression across the whole visible spectrum, while brightness looks only at a blue band around 457 nm.
Related terms
ISO brightness
Diffuse blue reflectance factor at 457 nm, measured with d/0 geometry and UV content matched to illuminant C.
TAPPI brightness
North American directional brightness measured with 45/0 geometry at 457 nm, widely called GE brightness.
R457
Notation for diffuse blue reflectance factor at an effective wavelength of 457 nm, the quantity behind brightness.
Whiteness
How white a surface looks to the eye, judged across the whole visible spectrum rather than one blue band.
Points
Mill shorthand for units of brightness, opacity or whiteness on their percentage or index scales.