Defined in ISO 2470-2, it keeps the d/0 geometry and 457 nm weighting of ISO brightness but calibrates the ultraviolet content to D65, which carries more UV than illuminant C. On a sheet with no optical brightener the two readings are nearly identical; on a heavily brightened office paper the D65 value can run several points higher. Mills selling brightened grades quote it because it reflects more of the brightener response seen in daylight.
New office grade reads 94 D65 brightness but only 89 ISO, so check which number sales printed on the data sheet.
On a sheet with no optical brightener, D65 brightness adds nothing over ISO brightness, so it is only worth quoting on brightened grades.
Also heard as
- ISO 2470-2 brightness
Related terms
ISO brightness
Diffuse blue reflectance factor at 457 nm, measured with d/0 geometry and UV content matched to illuminant C.
Illuminant D65
Standard CIE daylight at about 6500 K, with enough ultraviolet to excite optical brighteners strongly.
OBA
Optical brightening agent: a dye that absorbs UV light and re-emits it as blue, making paper look whiter.
Fluorescence
Light a sample emits after absorbing UV, measured in paper as the gap between UV-included and UV-excluded readings.