Whiteness
Also: CIE whiteness, whiteness index
A measurement of how white a paper appears, taking into account fluorescence from optical brighteners, distinct from brightness.
Whiteness is a broader optical measurement than brightness. It integrates reflection across the visible spectrum and accounts for fluorescent enhancement from optical brightening agents (OBAs). CIE whiteness, the dominant standard (ISO 11475), can exceed 100 when OBAs are present.
Whiteness and brightness are often confused. Brightness is a narrow-band measurement at 457 nm; whiteness is the full spectrum impression. A paper can have high brightness but low whiteness if it has a yellowish cast.
Related
- OBA (optical brightening agent). A chemical that absorbs UV light and re-emits visible blue light, making paper appear whiter and brighter than physics would allow without it.