Temporal dynamics of daylight perception: Detection thresholds

Abstract

Temporal changes in illumination are ubiquitous; natural light, for example, varies in color temperature and irradiance throughout the day. Yet little is known about human sensitivity to temporal changes in illumination spectra. Here, we aimed to determine the minimum detectable velocity of chromaticity change of daylight metamers in an immersive environment. The main stimulus was a continuous, monotonic change in global illumination chromaticity along the daylight locus in warmer (toward lower correlated color temperatures [CCTs]) or cooler directions, away from an adapting base light (CCT: 13,000 K, 6500 K, 4160 K, or 2000 K). All lights were generated by spectrally tunable overhead lamps as smoothest-possible metamers of the desired chromaticities. Mean detection thresholds (for 22 participants) for a fixed duration of 10 seconds ranged from 15 to 2 CIELUV E units, depending significantly on base light CCT and with a significant interaction between CCT and direction of change. Cool changes become less noticeable for progressively warmer base lights and vice versa. For the two extreme base lights, sensitivity to changes toward neutral is significantly lower than for the opposite direction. The results suggest a "neutral bias" in illumination change discriminability, and that typical temporal changes in daylight chromaticity are likely to be below threshold detectability, at least where there are no concomitant overall illuminance changes. These factors may contribute to perceptual stability of natural scenes and color constancy.

Improvements to the CIELUV color space

“…The values of parameters p 1 -p 9 obtained by the numerical solution of the optimization problem in (19), are listed in the last row of Table 1 and constitute a new color space named MLUV2. Note that Wang et al 29 found that the chromaticity coordinates u 0 m , v 0 m , associated to the color space obtained by solving the optimization problem in (15), predicted MacAdam's ellipses better than the u 0 , v 0 coordinates in terms of the LU measure, but not in terms of the GU measure.…”

“…Note that Wang et al 29 found that the chromaticity coordinates u 0 m , v 0 m , associated to the color space obtained by solving the optimization problem in (15), predicted MacAdam's ellipses better than the u 0 , v 0 coordinates in terms of the LU measure, but not in terms of the GU measure. For this reason, only the GU measure has been considered in Equation ( 18), along with the optimization problem posed in (19).…”

“…Here, and are determined using Equation (6) from tristimulus values , , of the reference white. Since the CIELUV color space incorporated the CIE 1976 uniform chromaticity scale diagram, and straight lines in the diagram readily express additive color mixture, the CIELUV color space is currently used in some industrial applications that depend on additive light mixing, such as color TV sets, video monitors, and lighting 7,14–19 …”

“…Since the CIELUV color space incorporated the CIE 1976u 0 v 0 uniform chromaticity scale diagram, and straight lines in the u 0 v 0 diagram readily express additive color mixture, the CIELUV color space is currently used in some industrial applications that depend on additive light mixing, such as color TV sets, video monitors, and lighting. 7,[14][15][16][17][18][19] Since 1976, CIELAB-based color differences formulas such as CMC, 20 CIE94, 21,22 and CIEDE2000 23,24 have been developed. Currently, the most accurate color difference formula available is CIEDE2000, which has been jointly recommended as a standard by ISO and CIE. 25 Unfortunately, however, there are no color spaces associated to any of these three color difference formulas.…”