EN ISO 18314-4:2024 PDF

Overview

EN ISO 18314-4:2024 - Analytical colorimetry, Part 4 - defines a formalism for quantifying illuminant metamerism of solid surface colours. The standard specifies how to calculate a metamerism index for pairs of samples when the illuminant changes, using colour-difference assessment in the CIELAB (Lab)* space. It applies to solid surfaces (not to effect coatings without metrical adaptation) and focuses solely on metamerism due to change of illuminant - the phenomenon most relevant for practical colour reproduction and quality control.

Key topics and technical requirements

• Metamerism index (Mt): Defined as the colour difference (ΔE) between two samples under a test illuminant when they match (ΔE = 0) under a reference illuminant. Mt provides a formal, reproducible measure of illuminant metamerism.
• Colour-difference assessment: Quantification is based on established ΔE evaluation methods in CIELAB coordinates (L*, a*, b*). Tolerances used for residual colour differences are applicable for specifying acceptable metamerism.
• Reference and test illuminants: Uses standard illuminants per ISO/CIE practices to compare conditions and compute differences.
• Correction methods: Guidance is provided for situations where chromaticity coordinates under reference conditions do not exactly match. Three correction algorithms are specified:
  • Additive correction
  • Multiplicative correction
  • Spectral correction
• Reporting requirements: The standard outlines data and test-report content to ensure consistent documentation of metamerism assessments.
• Scope limits: Not suitable for effect coatings without metrically adapting the method. The document distinguishes illuminant metamerism from observer and field-size metamerism.

Practical applications and users

EN ISO 18314-4:2024 is intended for professionals involved in colour formulation, measurement and quality assurance:

• Paints, coatings and pigments manufacturers - to quantify metamerism between color samples and matches.
• Textile, plastics and printing industries - for specifying tolerances and assessing colour reproduction under different lighting.
• Colour laboratories and QC departments - to standardize metamerism testing and reporting.
• Automotive, lighting and product design teams - to evaluate how colours will appear under real-world illuminants.
• Research and standards bodies - for comparative studies and method development in analytical colorimetry.

Using the metamerism index helps purchasers, suppliers and colorists specify acceptable colour behaviour across illuminants and reduce costly mismatches in finished products.

Related standards

Normative references inform implementation and include:

• ISO/CIE 11664-1 (CIE standard colorimetric observers)
• ISO/CIE 11664-2 (CIE standard illuminants)
• ISO/CIE 11664-4 (CIELAB Lab* colour space)
• CIE 015 (Colorimetry)

Keywords: EN ISO 18314-4:2024, metamerism index, illuminant metamerism, analytical colorimetry, CIELAB, colour difference, spectral correction, additive correction, multiplicative correction.