Optical brighteners absorb ultraviolet and re-emit it in the blue, so a brightened sheet can send back more blue light than falls on it in that band. Labs report the fluorescent component as brightness with UV included minus brightness with the UV cut filter in place. Its size depends on brightener dose, carrier, quenching additives and the UV content of the instrument or the viewing light.
Fluorescence is only 4 points on the new run against 9 on the old one, so go check the OBA pump.
Also heard as
- fluorescent component
Related terms
OBA
Optical brightening agent: a dye that absorbs UV light and re-emits it as blue, making paper look whiter.
UV cut filter
Filter that blocks wavelengths below about 420 nm so a sample can be measured without its fluorescence.
UV calibration
Setting an instrument's ultraviolet content so fluorescent samples read as they would under the specified illuminant.
Black light
Handheld or bench UV lamp used to check quickly whether a paper contains optical brightener.