Best lighting for visual appreciation of artistic paintings--experiments with real paintings and real illumination

In a previous study based on monitor simulations of artistic paintings, it was found that the average correlated color temperature (CCT) of daylight preferred by a large set of observers to illuminate paintings was around 5100 K. The goal of the present study was to test if this result holds in real viewing conditions, i.e., with real paintings and real light sources. The same 11 paintings were tested in real conditions illuminated by a spectrally tunable light source and with accurate monitor simulations. To ensure uniform illumination across the paintings, only a central part of the paintings was visible to the observers. It was found that the average CCT preferred for real and monitor viewing conditions were very similar, 5500 and 5700 K, respectively. The somewhat larger CCT obtained with monitor viewing in relation to the former study was only observed in some paintings and was attributed to the smaller viewing area. These results confirm that CCT for best appreciation of paintings is higher than normally used in museums, and the viewing conditions, real or simulated, have only a minor effect.

Effects of high-color-discrimination capability spectra on color-deficient vision

Light sources with three spectral bands in specific spectral positions are known to have high-color-discrimination capability. W. A. Thornton hypothesized that they may also enhance color discrimination for color-deficient observers. This hypothesis was tested here by comparing the Rösch-MacAdam color volume for color-deficient observers rendered by three of these singular spectra, two reported previously and one derived in this paper by maximization of the Rösch-MacAdam color solid. It was found that all illuminants tested enhance discriminability for deuteranomalous observers, but their impact on other congenital deficiencies was variable. The best illuminant was the one derived here, as it was clearly advantageous for the two red-green anomalies and for tritanopes and almost neutral for red-green dichromats. We conclude that three-band spectra with high-color-discrimination capability for normal observers do not necessarily produce comparable enhancements for color-deficient observers, but suitable spectral optimization clearly enhances the vision of the color deficient.

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.

Lighting spectrum to maximize colorfulness

The spectrum of modern illumination can be computationally tailored considering the visual effects of lighting. We investigated the spectral profiles of the white illumination maximizing the theoretical limits of the perceivable object colors. A large number of metamers with various degrees of smoothness were generated on and around the Planckian locus, and the volume in the CIELAB space of the optimal colors for each metamer was calculated. The optimal spectrum was found at the color temperature of around 5.7×10(3) K, had three peaks at both ends of the visible band and at around 510 nm, and was 25% better than daylight and 35% better than Thornton's prime color lamp.

Psychophysical optimization of lighting spectra for naturalness, preference, and chromatic diversity

The optimal spectral profiles of lighting for naturalness, individual preference, and chromatic diversity were estimated with psychophysical experiments in which observers selected illuminants from a set of metamers of D65 to render outdoor and indoor scenes. For naturalness, the illuminant selected was more spectrally structured than daylight and had a low color rendering index. For preference, the illuminant was similar but produced colors a little more saturated. For chromatic diversity, the spectrum was much more structured, with clearly defined peaks in the blue, green, and red spectral regions. These experiments show that light sources with specific structured spectra may have important visual applications in lighting.

Survival of Lactobacillus helveticus strain CP53 in the human gastrointestinal tract

A strain of Lactobacillus helveticus carrying the cryptic plasmid pCP53 was used for a detailed analysis of the survival and persistence of this organism in the faeces of volunteers administered oral doses of the strain. The CP53 strain had high affinity for Caco-2 cells, but displayed low bile acid resistance in vitro. Rifampicin-resistant colonies could be reisolated from the faeces of four of seven subjects fed with the rifampicin-resistant CP53 derivative strain. Moreover, the recovery of cells, as estimated by plasmid analysis, was higher than that estimated by measuring the number of rifampicin-resistant cells. From these results, we conclude that the CP53 strain can survive passage through the gastrointestinal tract.

Antihypertensive peptides are present in aorta after oral administration of sour milk containing these peptides to spontaneously hypertensive rats

Absorption of inhibitory peptides to angiotensin I-converting enzyme, L-valyl-L-prolyl-L-proline and L-isoleucyl-L-prolyl-L-proline, was studied in spontaneously hypertensive rats and normotensive Wistar-Kyoto rats after an oral administration of Calpis sour milk, which contains these peptides. Six hours after the administration of Calpis sour milk or saline to spontaneously hypertensive rats or normotensive Wistar-Kyoto rats, the blood pressure was measured and rats were killed. Abdominal aorta, lung, kidney, heart and brain were excised, homogenized and solubilized by detergent treatments. Angiotensin I-converting enzyme activity in the solubilized fractions from the abdominal aorta was significantly lower in spontaneously hypertensive rats given the sour milk than in the rats given saline. L-Valyl-L-prolyl-L-proline and L-isoleucyl-L-prolyl-L-proline were detected by HPLC in the heat-treated solubilized fraction from the abdominal aorta of spontaneously hypertensive rats given the sour milk. In contrast, the tripeptides were not detected in rats given saline, or in normotensive Wistar-Kyoto rats given the sour milk or saline. These data suggest that L-valyl-L-prolyl-L-proline and L-isoleucyl-L-prolyl-L-proline in the Calpis sour milk are absorbed directly without being decomposed by digestive enzymes, reach the abdominal aorta, inhibit the angiotensin I-converting enzyme, and show antihypertensive effects in spontaneously hypertensive rats.

Decrease of tissue angiotensin I-converting enzyme activity upon feeding sour milk in spontaneously hypertensive rats

Blood pressure increases were inhibited by feeding a diet containing sour milk fermented by a starter containing Lactobacillus helveticus and Saccharomyces cerevisiae to spontaneously hypertensive rats. In rats fed with the sour milk, the angiotensin I-converting enzyme activity of the aorta was significantly lower than that of rats fed with the control commercial diet.