LAB colour values are the numerical language of professional colour management. When a spectrophotometer measures a colour and produces a result, those results are most commonly expressed in the L\*a\*b\* colour space — a three-dimensional model of colour developed by the International Commission on Illumination (CIE) in 1976. Understanding LAB values is essential for anyone working with X-Rite instruments, colour specifications, or quality tolerance documents, because LAB is the common language in which colour differences are described, compared, and controlled across virtually every professional colour application.
The LAB colour space was specifically designed to overcome a fundamental limitation of other colour models like RGB or CMYK: it is device-independent and approximately perceptually uniform. Device independence means that LAB values describe a colour in absolute terms — a set of LAB values represents the same colour regardless of the device, process, or material used to produce it. Perceptual uniformity means that equal numerical differences in LAB space correspond to approximately equal perceived colour differences — the same numerical gap looks the same distance apart to a human eye, across different areas of the colour space. This makes LAB the ideal foundation for colour difference calculations like Delta E.
The Three Axes of LAB
The L\*a\*b\* colour space uses three axes to define any colour:
**L\* (Lightness)**: The vertical axis of the colour space, ranging from 0 (pure black) to 100 (perfect white). L\* describes how light or dark a colour is, independent of its hue or saturation. A bright lemon yellow and a dark forest green may share similar hue characteristics, but they have very different L\* values. In production colour control, monitoring L\* is important for catching issues like fading, over-dilution of pigment, or substrate colour variation that affect overall lightness without necessarily shifting the hue.
**a\* (Red-Green axis)**: This axis runs from negative values (green) to positive values (red). A neutral grey has an a\* value near zero. A saturated red paint might have an a\* value of +45 or higher; a saturated green might be -35 or lower. When a measured colour shows a positive a\* deviation from its target, it is trending too red (or not green enough). This directional information, available immediately from any X-Rite spectrophotometer, tells an operator which way to adjust.
**b\* (Yellow-Blue axis)**: This axis runs from negative values (blue) to positive values (yellow). Neutral grey is near zero on the b\* axis as well. A warm yellow has a high positive b\* value; a cool blue has a strong negative b\* value. In printing, a positive b\* shift often indicates that an ink is laying down with a warmer, more yellow cast than the target — perhaps due to ink temperature, viscosity changes, or substrate yellowing.
Using LAB in Colour Specifications and Tolerances
LAB values appear throughout colour specifications and quality control documents. A brand's colour specification might state: "Target: L\* 45.2, a\* 52.1, b\* 38.4. Tolerance: ΔE2000 ≤ 2.0." This completely defines the target colour and the acceptable range of variation in objective, universally understood terms. Any production facility with a calibrated spectrophotometer can measure against this specification and produce a documented pass/fail result — regardless of geography, substrate, or process type.
This universality is precisely why LAB has become the standard colour language for global supply chains. A brand owner in London can specify a colour in LAB terms, a packaging converter in Melbourne can measure against it using a Ci64 handheld spectrophotometer, and both parties are working from exactly the same colour definition. There is no ambiguity about what the target is, and no room for the kind of "close enough" visual judgement that creates colour disputes between brand owners and their suppliers.
The eXact 2 spectrophotometer stores colour targets in LAB terms and reports measurement results showing both the target values and the measured values side by side, along with the ΔL\*, Δa\*, Δb\* differences and the overall ΔE. This immediate display of directional colour difference data gives press operators the specific adjustment information they need, rather than just a pass/fail status that tells them something is wrong without indicating what to fix.
LAB and Colour Communication
Beyond quality control, LAB values serve a broader communication function in colour work. When a designer wants to specify a colour precisely for production, they can use LAB values alongside or instead of a Pantone reference — providing a numerical description that is unambiguous and substrate-independent. When a brand owner is moving a colour from one substrate to another (from paper to plastic, for example), LAB values provide the linking reference that connects the two substrate-specific specifications to a single colour identity.
The Pantone products sold through Seaga Group include LAB values for every Pantone colour in their library, providing a direct bridge between the familiar Pantone reference system and the LAB-based measurement world. Every Pantone number maps to specific LAB values, allowing anyone with a spectrophotometer to measure whether a produced colour achieves the Pantone target in objective, LAB-based terms.
Conclusion
LAB colour values are the foundation of modern colour communication and quality management. They provide a universal, device-independent, perceptually meaningful description of colour that can be used as a specification, a measurement result, a tolerance boundary, and a basis for colour difference calculation. Understanding L\*, a\*, and b\* — what each axis means, how they combine to describe any colour, and how they relate to Delta E — is fundamental to using X-Rite instruments effectively and to participating in professional colour management workflows in any industry.