Whiteness is not simply high L*. A white sample can look cleaner, bluer, creamier or greyer than another sample with similar lightness. A whiteness index combines measured tristimulus or chromaticity data into one number intended for a defined family of near-white materials.
What a whiteness index means
Higher values generally indicate a whiter appearance within the range and conditions for which the chosen formula is valid. Many systems also report tint, which helps distinguish a reddish or greenish cast that one whiteness number can hide. The index is a calculated quality metric, not a directly measured wavelength and not a universal ranking for every pale color.
| Reported item | What it contributes |
|---|---|
| Whiteness index | A combined assessment of lightness and chromatic deviation for near-white samples. |
| Tint | Additional information about the direction of a subtle color cast. |
| Spectral curve | Evidence of where reflectance or fluorescence differences occur across wavelength. |
Why the formula and settings matter
Name the equation, not only “whiteness index.” CIE whiteness is commonly reported as W or W10 under D65 with the 10° observer and is intended for near-white samples within its stated whiteness and tint validity limits. ASTM E313, Ganz–Griesser, Berger, Stensby and Hunter indices are different scales and can produce different numbers on the same specimen. Results from different equations should not share one tolerance. Geometry, specular treatment, backing, number of layers and sample preparation can also alter the value, so state the complete method in the specification and instrument software.
Fluorescent whitening agents need UV control
Optical brighteners absorb ultraviolet energy and emit visible blue light, making a material appear whiter. Their contribution depends on the physical UV content used during measurement. Selecting D65 as a calculation illuminant does not by itself reproduce a controlled D65 UV stimulus. If brighteners are present, define the instrument’s UV condition, calibration procedure and reference standards.
Use whiteness only inside its valid region
A whiteness formula designed for near-white samples can become misleading for strongly colored or unusually tinted materials. Keep component L*, a*, b* or spectral checks where they add necessary control.
A defensible QC workflow
01
Choose the standard
Use the formula and conditions required by the product, customer or industry method.
02
Control presentation
Fix backing, thickness or layers, orientation, aperture and UV condition.
03
Compare like with like
Use the approved standard, trend tint and component values, and investigate drift.
See also CIELAB, standard illuminants and color standards for quality control.
Last reviewed 21/09/2026 · Level: Intermediate
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