Chromatic Effects of Metamers of Daylights

Sérgio M.C. Nascimento, Paulo E.R. Felgueiras,
João M.M. Linhares
University of Minho, Portugal
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The relationship between the spectral composition of light sources and the visual appearance of rendered scenes is a matter of practical relevance and assumes today particular significance with the advent of light sources of almost arbitrary spectral distribution, like modern LED based lighting. This relationship has only been studied for specific illuminants, like daylights, and systematic studies with other light sources are necessary.
The aim of this work was to address this issue by studying, computationally,
some chromatic effects of metamers of daylight illuminants. For each daylight with correlated color temperature (CCT) in the range 25000 K – 4000 K a large set of metamers was generate using the Schmitt’s elements approach. The metamers set was parameterized by the absolute spectral difference to the equienergy illuminant E and by the number of non-zero spectral bands. The chromatic effects of the metamers were quantified by the CIE color rendering index CRI and by the CIELAB color gamut generated when rendering the Munsell set. It was found that although CRI decreases with ∂, that is, as the illuminant spectrum becomes spectrally more structured, the largest values for the color gamut could be obtained only for large values of ∂. Furthermore, the relationship between color gamut and number of non-zero bands showed that the largest gamuts were obtained with a small number of spectral bands. Thus, spectrally structured metamers produced low CRI but larger color gamuts, a result suggesting that appropriate spectral tuning may be explored in practical illumination when obtaining
large chromatic diversity may be important.