What Is Metamerism? Why Does Color Change Under Different Light Sources?
Metamerism and color change under different light sources
What Is Metamerism? Why Does Color Change Under Different Light Sources?
Two samples may look nearly identical under one light source yet show a clear color difference under another. This phenomenon is called metamerism. It is usually not a measurement error: the samples have different spectral reflectance characteristics.
1. Why does metamerism happen?
The color we see results from both the illumination and the sample’s spectral reflectance. Two samples can appear similar under D65 while having different reflectance curves. When the light source changes, the energy at each wavelength changes too, so colors that once looked alike may diverge.
Example: two plastic parts made with different pigments or masterbatch formulations may look almost identical under D65. Under warm indoor or retail lighting, one may appear redder, yellower or bluer.
2. Why can colors still differ under another light even when ΔE is small?
ΔE describes the difference between two colors under a particular measurement condition. It does not guarantee that their appearance will match under every illuminant. If their spectral reflectance differs, a small ΔE under one light can coexist with a noticeable difference under another. A close match under D65 does not guarantee a close match under A, TL84 or other lighting.
3. Ordinary color difference vs. metamerism
Ordinary color difference: asks whether two samples differ under fixed conditions; the difference is visible under the same light; typical data include L*a*b* and ΔE; control it with consistent measurement conditions and acceptance limits.
Metamerism: asks whether the relationship between two samples changes when the illuminant changes; samples look close under one light but diverge under another; examine spectral reflectance, multiple illuminants and real appearance; assess it with multi-light comparisons and spectral analysis.
4. Products that may be affected
Textiles, apparel and footwear: fabrics, zippers, leather and mixed-material panels may match in factory lighting but differ in a store or outdoors.
Plastics and injection-molded parts: different masterbatches, resins, pigments or supplier formulations may create similar appearances but different reflectance spectra.
Coatings and inks: pigments that match under one source may shift under another.
Printing and packaging: paper, ink, plastic film and packaging materials can make brand colors vary with lighting.
Automotive interiors and exteriors: plastic, leather, fabric, paint and trim should be checked for consistency across illuminants.
Consumer products: bottles, caps, printing, cartons and contents made of different materials can also show multi-light mismatches.
5. What do a spectrophotometer and a light booth do?
They serve different, complementary purposes. A spectrophotometer captures spectral reflectance data, compares the spectral characteristics of samples and helps analyze possible color changes across illuminants. A standard light booth provides a controlled visual environment for directly comparing samples under specified sources such as D65, A and TL84.
6. Why are D65, A and TL84 commonly used?
Different sources have different spectral energy distributions, so the same sample may look different under each. Select illuminants according to the product’s real-use environment and customer acceptance conditions.
D65: a common standard daylight condition, used for general comparison and daylight-related evaluation.
A: a warm standard illuminant, useful for observing appearance under warm lighting.
TL84: one common comparison condition in commercial and retail lighting; use it when relevant to the application or customer requirements.
Customer-specified source: reflects the final use or inspection environment; supply-chain partners should use consistent viewing conditions.
7. How to investigate a color mismatch after changing light
Identify and record the light source where the difference appears, such as D65, TL84, warm lamps or store lighting. Keep an agreed master sample and compare it with the disputed production lot. Compare samples under multiple illuminants using the same viewing conditions. If needed, review L*a*b*, ΔE and spectral reflectance data. Check whether pigments, masterbatch, ink, substrate, supplier or process lot changed. For products prone to metamerism, document the agreed illuminants and viewing conditions in the acceptance standard.
Is metamerism the same as SCI/SCE?
No. Metamerism concerns whether the color relationship between samples changes under different illuminants. SCI/SCE describes how specular reflection is handled during measurement and is mainly related to the effect of surface gloss on results.
Frequently asked questions
What is metamerism?
Two samples look similar under one light source but differ more noticeably under another.
Why can colors differ under a new light when ΔE is small?
A ΔE measured under one illuminant cannot represent appearance under all illuminants. Different reflectance spectra can cause the color relationship to change.
Can a light booth check metamerism?
A light booth provides a controlled multi-illuminant environment for visual comparison. Spectral data can help investigate the cause.
If a sample passes under D65 but differs under TL84, is it automatically rejected?
Not necessarily. Requirements depend on product specifications, customer standards and the actual use environment.
Color changes after switching light sources?
Provide the master and disputed samples, material information, illuminants and available color data so the cause can be assessed.
Contact Fulcrum Technology | Spectrophotometers | Standard light booths for color assessment