CIE L*a*b*—also called CIELAB or Lab—is the color space behind many quality-control decisions. It describes a color using three coordinates: L* for lightness, a* for the red–green axis and b* for the yellow–blue axis. Once you can read those three numbers, color data becomes much easier to use.
What is CIE L*a*b*?
CIE L*a*b* is a device-independent color space developed by the International Commission on Illumination (CIE). It was designed so the numerical distance between colors relates more closely to the differences people can see than earlier coordinate systems. It is distinct from Hunter Lab, an earlier color scale that some instrument software also offers—the two are not interchangeable and produce different numbers for the same sample.
A spectrophotometer measures a sample’s spectrum, then calculates L*a*b* under a stated illuminant and standard observer. Those conditions are part of the result. “L* 55, a* 18, b* 24” is incomplete unless the measurement method and settings are controlled too.
L* / LIGHTNESS
Black to white
L* is scaled so that 0 represents ideal black and 100 corresponds to a perfect reflecting diffuser under the stated conditions. Fluorescent or optically brightened samples can legitimately produce values slightly above 100. A lower L* means a darker sample; a higher L* means a lighter one.
a* / RED–GREEN
Green through neutral to red
Negative a* values lean green. Positive a* values lean red. Values near zero have little red–green bias.
b* / YELLOW–BLUE
Blue through neutral to yellow
Negative b* values lean blue. Positive b* values lean yellow. Values near zero have little yellow–blue bias.
How to read L*, a* and b* values
The fastest way to interpret Lab values is to compare a measured sample with the approved standard. Look at the direction of each difference before you focus on the total ΔE.
| If the sample changes… | What it means visually | Typical process question |
|---|---|---|
| L* increases | The sample is lighter. | Has opacity, film thickness, pigment strength or drying changed? |
| L* decreases | The sample is darker. | Is there over-pigmentation, contamination or a surface-effect change? |
| a* increases | The sample is redder / less green. | Has the red pigment, dye or undertone shifted? |
| b* increases | The sample is yellower / less blue. | Has yellowing, optical brightener response or substrate variation changed? |
A coordinate movement describes direction, not acceptability. Use ΔE and the agreed tolerance to decide whether the sample passes.
How do L*a*b* values relate to ΔE?
ΔE is the calculated difference between two colors in a color space. In the simplest form, ΔE76 combines the differences in L*, a* and b* into one distance. That makes it useful for a fast indication, but it does not tell you why the sample differs.
The component differences are often written as ΔL*, Δa* and Δb*. They make troubleshooting more useful: ΔE may say a batch is out of tolerance, while the individual values show whether it is mainly too dark, too red or too yellow. For formulas and tolerance choices, see our practical ΔE guide.
Use total difference and direction together
A low ΔE can still be a problem if it moves in a visually sensitive direction for your product. Recording ΔL*, Δa* and Δb* helps color teams spot process drift before the total value crosses the limit.
Why the measurement method still matters
CIE L*a*b* does not remove the need for a controlled method. Two readings can differ when the instrument, geometry, aperture, illuminant, observer, calibration, backing, sample orientation or averaging routine changes.
- Illuminant: D65, A and F-series settings represent different lighting conditions. Choose the one required by the customer or standard.
- Observer: 2° and 10° standard observers can produce different coordinates, especially for some materials and colors.
- Geometry: d/8° and 45°/0° instruments treat gloss and surface appearance differently.
- Sample presentation: Texture, curvature, translucency, backing and measurement location can be as important as the formula.
A good color specification therefore names the instrument conditions alongside the L*a*b* target and ΔE limit. If it does not, agreeing a test method is the first step toward useful correlation.
Where CIELAB is used
Paints & coatings
Track batch direction, formulation trials and finish changes alongside the total color difference.
Plastics
Compare resin, masterbatch and moulded parts while isolating shifts in lightness or undertone.
Textiles & print
Communicate shade, spot-color and production-run differences with a shared numerical language.
Food, powders & materials
Measure color change in products where visual consistency supports quality and consumer confidence.
A practical CIELAB workflow
- ✓ Calibrate the instrument using the manufacturer’s routine.
- ✓ Measure an approved standard using the specified geometry, illuminant and observer.
- ✓ Measure the sample in the same position and orientation, averaging where the method requires it.
- ✓ Review ΔL*, Δa* and Δb* before relying on total ΔE alone.
- ✓ Record the method with the result so another team can reproduce it.
This workflow turns Lab from a reporting format into a practical control tool. If you are still deciding which device supports your method, start with what a spectrophotometer measures and compare it with a colorimeter before choosing.
Frequently asked questions
What is a good L*a*b* value?
There is no universally good Lab value. The correct numbers are the approved target for your material, finish and viewing conditions. Quality control compares the sample with that target, not with a generic ideal.
Is CIELAB the same as Lab?
In industrial color measurement, “Lab”, “L*a*b*” and “CIELAB” are commonly used to refer to the same CIE color space, but confirm the software is not reporting Hunter Lab. Confirm the illuminant and observer too, because those settings are essential context.
Can a colorimeter measure L*a*b*?
Many colorimeters can report L*a*b*. A spectrophotometer additionally retains spectral data, which is more useful when you need flexible calculations, tight correlation, metamerism investigation or multi-illuminant analysis.
Last reviewed 21/09/2026 · Level: Fundamental
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