Best lighting for naturalness and preference

Spectral optimization for naturalness and preference was carried out empirically in a set of psychophysical experiments in which observers adjusted the spectral composition of the illumination to render commercial food counters containing a variety of fruits and vegetables as well as meat and fish. The scenes were simulated with high chromatic precision on a calibrated computer monitor from data obtained by hyperspectral imaging. The illuminants were daylight-like and their metamers, representing a set of nearly arbitrary spectra. For daylights, the most natural colors were produced with illuminants with an average correlated color temperature (CCT) of 6040 K and the most preferred colors with an average CCT of 4410 K. For metamers, the CCT for the two conditions were a little higher than for daylights, and the corresponding spectra were considerably different from daylight with characteristic peaks at both ends of the visible band and at about 490 nm and 560 nm. When compared directly with daylights, these metamers were preferred for most of the scenes. It was hypothesized that observers' choices may be determined by the chromatic volume and the symmetry of the color distributions: The best illuminants for preference produced larger gamuts, and the best illuminants for naturalness produced gamuts with aspect ratios closer to unity, i.e., more symmetrically distributed.