Walk into a clothing store and pick a shirt that looks like a perfect navy blue under the fluorescent lights. Take it outside into daylight and it might look almost black. Take it home under your warm LED downlights and it could appear to have a slight purple cast. The shirt has not changed — but your perception of its colour has, dramatically, simply because the light source changed. This phenomenon is not an optical illusion or a quirk of human psychology. It is fundamental physics, and it has enormous practical consequences for any business that needs to manage colour consistently.
The colour that a surface appears to have is not an intrinsic property of the surface — it is the product of the interaction between the surface's reflectance properties and the light that illuminates it. Different light sources have very different spectral compositions. Daylight contains a relatively broad, balanced distribution of wavelengths across the visible spectrum. Fluorescent light has a characteristic spike pattern, with strong emission at certain wavelengths. LED sources vary widely depending on their design — warm white LEDs are rich in yellow and red wavelengths, while cool white LEDs emphasise blue. Each of these different illuminant spectra interacts differently with the surface reflectance properties of any given colour, producing a different perceived result.
For colour quality control, this means that a visual colour assessment is only valid for the specific light source under which it was made. An inspector who approves a colour under fluorescent factory lighting cannot guarantee that the colour will look acceptable to the consumer under their home LED lighting, to the retail buyer under their store's display lighting, or to the brand owner under D50 standardised daylight. Each of these viewers will see a potentially different colour — and the riskiest scenario is when the different light sources reveal a colour difference that was invisible under the factory's lighting.
Metamerism: The Colour That Changes With the Light
The most problematic manifestation of lighting effects on colour is metamerism — the phenomenon where two colour samples appear identical under one light source but noticeably different under another. Metameric pairs arise when two colours with different spectral reflectance curves happen to produce the same tristimulus response (the same L\*a\*b\* values) under a specific illuminant, but produce different responses under another illuminant with a different spectral power distribution.
Metamerism is a well-known problem in packaging, textile, and plastics manufacturing. A package produced with a specific ink formulation might match the approved standard beautifully under D65 daylight simulation, but show a clear mismatch under the A-illuminant (incandescent) or UV-rich fluorescent conditions present in some retail environments. A moulded plastic component matched to its housing under one light source might fail to match under another. In these cases, visual approval at the production site provides no guarantee of acceptable appearance at the point of use.
X-Rite spectrophotometers address metamerism by measuring the full spectral reflectance curve of both the sample and the reference, then calculating colour difference values under multiple illuminants simultaneously. If two samples are metameric — matching under one illuminant but not another — the spectral data reveals this: the reflectance curves are different even when the colour values under a single illuminant are identical. The benchtop spectrophotometers in X-Rite's range are particularly useful for metamerism analysis in colour formulation laboratories.
Standardised Viewing Conditions
Because lighting conditions are so critical to colour assessment, the industry has developed standardised light sources for visual colour evaluation. The most important is D50 — a simulated daylight standard with a correlated colour temperature of 5000K, defined by the CIE and used as the reference illuminant for graphic arts and printing colour work. D65 (6500K daylight simulation) is used in some industries, and A (2856K incandescent) is included in many light booth specifications for checking metamerism.
X-Rite's range of light booths provides standardised D50, D65, A, F2 (cool white fluorescent), and UV-supplemented illumination in a controlled viewing environment. The Judge LED light booth uses LED technology to deliver precise, stable illumination at each standard, while the Spectralight QC uses filtered tungsten halogen sources for applications where traditional illuminant simulation is required. Using a light booth alongside an X-Rite spectrophotometer gives quality control teams both objective numerical measurement and standardised visual evaluation — a combination that covers every aspect of professional colour approval.
For production environments where formal visual assessment is part of the colour approval workflow, standardised lighting is not optional. A colour passed under non-standardised factory lighting is an unverified colour. A colour passed under a calibrated D50 light source is a colour that has been evaluated according to the same standard that the customer, the brand owner, and the international quality auditor will use.
Conclusion
Lighting conditions are not a peripheral consideration in colour management — they are central to how colour appears, how it is assessed, and how consistent it will look across the different environments in which a product is viewed. Understanding the physics of illuminant-dependent colour appearance, the risk of metamerism, and the importance of standardised viewing conditions is essential background for anyone building a professional colour management program. X-Rite's combination of spectrophotometers for objective measurement and standardised light booths for visual evaluation provides the complete toolkit for managing colour correctly under all relevant conditions.