OBA (optical brightening agent)
Also: OBA, optical brightening agent, fluorescent whitener, FWA
A chemical that absorbs UV light and re-emits visible blue light, making paper appear whiter and brighter than physics would allow without it.
OBAs are stilbene-based fluorescent molecules added to the wet end or coating of white paper. They absorb UV radiation in the 340 to 380 nm range and re-emit it as visible blue light around 420 to 440 nm, compensating for the natural yellowish cast of wood fiber. Paper with OBA can have CIE whiteness values above 150 under full daylight.
OBAs are sensitive to storage conditions and UV exposure: papers made with heavy OBA can yellow faster in sunlight than OBA-free papers. Archival paper grades explicitly avoid OBAs.
Related
- Whiteness. A measurement of how white a paper appears, taking into account fluorescence from optical brighteners, distinct from brightness.