Directional geometry imitates how a reader holds a printed page under a lamp, with the mirror reflection angled away from the eye. TAPPI brightness and most graphic arts color measurement use it. Because the light arrives from one direction, readings respond to surface texture, felt marks and grain, so instruments either light the sample from a full ring of 45-degree angles or the operator averages readings at several rotations.
Pressroom reads paper white on a 45/0 handheld, so their numbers will never line up with our d/0 bench readings.
Also heard as
- 45/0
- 0/45
- directional geometry
Related terms
TAPPI brightness
North American directional brightness measured with 45/0 geometry at 457 nm, widely called GE brightness.
d/0 geometry
Measurement setup with diffuse illumination of the sample and viewing perpendicular to its surface.
Spectrophotometer
Instrument that measures reflectance across the visible spectrum and computes brightness, whiteness, opacity and color.