CIE L*a*b* Colour Space and Colour Difference Measurement
topic
CIE L*a*b* (CIELAB) colour space (ISO 11664-4, CIE Publication 15) provides a three-dimensional, approximately perceptually uniform representation of all visible colours with L* = 0 (perfect black) to L* = 100 (perfect white), a* from −128 (green) to +128 (red), b* from −128 (blue) to +128 (yellow) — measured from spectrophotometric reflectance curve under standardised D65/10° illuminant/observer combination. Instrument measurement protocol for textile colour: 4 readings per specimen (rotating 90° between readings) averaged to eliminate directionality from fabric texture; SCE mode (specular component excluded) standard for apparel colour assessment (removes specular gloss contribution from colour measurement); SCI mode (specular included) for whiteness and optical brightener assessment. Colour difference calculation: ΔE*ab = √(ΔL*² + Δa*² + Δb*²) — simple Euclidean distance in L*a*b* space; ΔE*00 (CIEDE2000) corrects for perceptual non-uniformities in L*a*b* space using rotation terms (RT) and weighting functions for lightness (SL), chroma (SC), hue (SH) — ΔE*00 better predicts human colour perception in commercial textile colour assessment (R² = 0.92 versus R² = 0.78 for ΔE*ab in paired comparison studies). Commercial colour tolerance: luxury fashion ΔE*00 < 0.5 (tight match required); mid-market apparel ΔE*00 < 1.0; casual budget fashion ΔE*00 < 1.5; household textiles ΔE*00 < 2.0 — tolerance ellipses in L*a*b* space are elongated along hue axis (larger hue difference tolerated than chroma or lightness difference of equal magnitude). Metamerism index (MI): two fabrics matching under D65 may differ under A (tungsten) or F11 (fluorescent) illuminants — MI (ISO 23603) = ΔE*00 between sample and standard under test illuminant versus reference illuminant: MI < 1.0 = negligible metamerism, MI > 3.0 = severe metamerism causing visible mismatch under fluorescent retail lighting versus standard D65 assessment — metamerism from different dye recipe achieving same L*a*b* under D65.
Role
CIE L*a*b* colour measurement and ΔE*00 calculation is the universal quantitative language of textile colour quality management — replacing subjective visual pass/fail decisions with objective numeric colour tolerances that enable consistent colour approval across global brand offices, sourcing regions, and laboratory environments, making instrumental colour communication the foundational technology for the $20 billion global colour management services and instruments market serving textile and apparel supply chains.