FAQ – Could I Get a Quick Rundown of Why I Might Use Different Illuminants, and If I Would Ever Need To?
Answer
Yes. Different illuminants simulate different lighting conditions and can significantly affect how a product appears. Most color measurement applications use Illuminant D65, which represents average daylight and is the most commonly specified illuminant worldwide. However, some industries, customers, or applications may require alternative illuminants to better represent the lighting conditions under which a product will actually be viewed.
Understanding the Concept
An illuminant is a mathematical model of a light source used to calculate color values from a measured spectrum. Common illuminants include:
- D65 – Average daylight (most common).
- A – Incandescent/tungsten lighting.
- C – Older daylight standard (largely replaced by D65).
- D50 – Horizon daylight, commonly used in printing and graphic arts.
- F2 – Cool white fluorescent lighting.
- F7 – Daylight fluorescent lighting.
- F11 – Narrow-band fluorescent lighting commonly found in commercial environments.
Because different light sources contain different amounts of energy at different wavelengths, the same product can appear differently under different illuminants.
When Might I Use Different Illuminants?
Most users never need to change illuminants because their specifications are already defined using D65. However, alternative illuminants may be useful when:
- A customer specification requires a specific illuminant.
- Products are primarily viewed under retail lighting.
- Products are viewed under office or fluorescent lighting.
- Printing and packaging applications require D50.
- Evaluating metamerism is important.
- Comparing appearance under multiple lighting conditions.
Common Misconceptions
"The Illuminant Changes the Measurement"
Not exactly.
The spectrophotometer measures the sample's spectral reflectance or transmittance. The illuminant is then applied mathematically during color calculation. The physical measurement does not change; only the calculated appearance under the selected lighting condition changes.
"Everyone Should Use the Same Illuminant"
Not necessarily.
The best illuminant is often the one specified by the customer, industry standard, or application. That said, D65 is the most widely used illuminant in modern industrial color measurement and is generally the default recommendation unless another illuminant is specifically required.
"Changing Illuminants Fixes Color Problems"
Changing illuminants does not improve color consistency. It simply changes how the color data is interpreted and reported.
Why It Matters
Different illuminants can reveal differences that may not be visible under another lighting condition. This is especially important when:
- Evaluating metameric color matches.
- Producing products viewed under multiple lighting environments.
- Working with textiles, coatings, plastics, packaging, and printed materials.
- Verifying customer color specifications.
- Investigating customer complaints related to appearance.
In many industries, color specifications are defined using a specific illuminant to ensure that all suppliers and manufacturers evaluate color under the same viewing conditions.
Key Takeaway
For most applications, Illuminant D65 is the preferred and most commonly used illuminant, and many users never need to change it. Alternative illuminants are typically used only when required by a customer specification, industry standard, or specific viewing environment. The illuminant does not change the measured spectrum—it changes how the measured color is calculated and reported under different lighting conditions.
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To learn more about Color and Color Science in industrial QC applications, click here: Fundamentals of Color and Appearance