The 2° and 10° standard observers are CIE color-matching functions used to turn spectral data into color values. They are not aperture sizes, instrument viewing-angle settings or the 8° observation angle in d/8° geometry.
What the observer represents
The CIE 1931 2° Standard Observer and CIE 1964 10° Standard Observer represent different visual fields used in colorimetric calculations. Software combines the measured spectrum with an illuminant and one of these observer functions to calculate XYZ, then can derive L*a*b*.
Keep the concepts separate
Geometry describes the source/sample/detector arrangement. Aperture describes the usable measurement area. The observer is a calculation function. All can affect the reported result, but they are different settings.
How to record the condition
A result such as “D65/10°” means D65 was used for the calculation and the 10° observer was selected. It does not specify geometry, SCI/SCE, aperture or ΔE formula, so those conditions still need to be recorded.
Neither observer is universally more accurate. Use the customer, industry or validated internal method, and use the same condition for the standard and sample. The same non-fluorescent spectrum can yield different coordinates under 2° and 10° because the calculation functions differ.
Read CIE L*a*b* explained and standard illuminants before defining a method. The CIE observer reference is the primary definition.
Last reviewed 21/09/2026 · Level: Fundamental
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