Paper whiteness affects the color of every transparent printing ink placed above it. Yet whiteness is often confused with brightness or a simple L* value. A defensible specification names the exact calculation and the instrument’s UV calibration, then controls the sheet stack, side, direction and moisture condition.
Choose the property you actually need
| Quantity | What it indicates |
|---|---|
| CIE whiteness | A full visual-whiteness assessment derived from tristimulus values and a tint component under a named illuminant and observer. |
| ISO brightness | Diffuse blue reflectance near 457 nm under the indoor-daylight UV condition defined by ISO 2470-1. |
| D65 brightness | Diffuse blue reflectance under the higher-UV D65 condition of ISO 2470-2. |
| L* | Perceptual lightness in CIELAB; useful, but not a substitute for whiteness or brightness. |
Control ultraviolet energy
Optical brightening agents absorb ultraviolet energy and emit visible blue light. The same sheet can therefore return different whiteness and brightness values when instruments deliver different UV content. Use an instrument and fluorescent reference appropriate to the specified method, and record whether the condition represents C, D65, M1 or UV-cut measurement. Do not compare unlike conditions as if they were repeat tests.
Prepare a representative specimen
- Condition samples at the temperature and humidity required by the paper method or purchasing specification.
- Identify top and wire/felt sides where they differ.
- Use the specified number of sheets or an opaque stack so backing does not influence the result.
- Avoid watermarks, dirt, folds, edges and handling contamination.
- Keep machine direction and instrument orientation consistent if the sheet is directional.
Measure several positions across and along the sheet or reel. Paper formation, coating and OBA application can vary spatially; one reading can hide a streak or lane difference that later shifts printed color.
Separate average from uniformity
Report the mean, range and, where useful, standard deviation. Compare sides and production lanes separately. If two lots have similar whiteness but print differently, inspect their spectral curves, tint, gloss, opacity, coating and ink holdout rather than increasing the whiteness tolerance alone.
Write a transferable paper specification
Name the standard, property, UV condition, geometry, reference calibration, backing or sheet count, side, conditioning, locations, averaging and tolerance. Pair whiteness with color coordinates and opacity when those properties affect the print. Continue with optical brighteners and UV, paper opacity and D50 vs D65.
Last reviewed 22/09/2026 · Level: Intermediate
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