The symbol names the measurement itself: reflectance factor weighted by a function that peaks near 457 nm with a half-width of roughly 44 nm. Written alone it usually means the reading on an opaque pad, which becomes ISO brightness when the UV content is set to illuminant C. Lab reports use it when they want to show the raw value without tying it to one brightness standard.
Logged R457 for both sides of the pad, and the wire side is a full point lower than the felt side.
Also heard as
- blue reflectance factor
Related terms
Brightness
The blue-light reflectance of pulp or paper, read at an effective wavelength of 457 nm and reported as a percentage.
ISO brightness
Diffuse blue reflectance factor at 457 nm, measured with d/0 geometry and UV content matched to illuminant C.
Reflectance factor
How much light a sample sends back compared with an ideal white diffuser lit and viewed the same way.
R-infinity
Reflectance factor of a pad so thick that adding more sheets no longer changes the reading.