Past studies have shown that the Feeling of Contrast Index (FCI) correlates with preference in some circumstances, but the exact relationship is not clear and may differ among visual conditions and targets. This paper presents a psychophysical experiment in which 70 observers evaluated the colour quality of natural objects under different spectral power distributions with different values of FCI but the same correlated colour temperature (3000 and 5000 K). Results show that FCI holds a nearly perfect linear correlation with vividness (r = 0.976); unnaturalness associated with enhanced vividness rendered by excessively high FCI deteriorates preference. These effects are independent of correlated colour temperatures, but are dependent upon the visual targets used because of limitations in the derivation of FCI. Compared to other metrics, FCI can characterise vividness under a light source.
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