Abstract
We present a spectral dataset of daylights and surface reflectances and transmittances of natural objects measured in Japan. Daylights were measured under the sun and under shadow from dawn to dusk on four different days to capture their temporal spectral transition. We separately measured daylight spectra at five different locations (including an open space and a forest) with minimum time difference to reveal whether a local environment alters daylight spectra reaching the ground. We found that colors of natural objects were spread in a limited area of color space, and data points were absent around saturated green regions. Daylight spectra were found to have a larger variation across time, weather, and local environments than previously thought. Datasets are made freely available, expanding past public datasets mainly collected in Northern America and Europe.
Highlights
The spectral shape of light reaching our eyes in everyday life is primarily determined by the spectral composition of daylights and the surface properties of objects that reflect and transmit the illuminant
Fig. 4. 307 natural objects whose spectral reflectance was used for analysis
Our results generally show agreement with the widely used Commission internationale de l’éclairage (CIE) daylight model, but disagreement around high color temperature regions and the influence of local environments on the effective daylight spectra should be noted
Summary
The spectral shape of light reaching our eyes in everyday life is primarily determined by the spectral composition of daylights and the surface properties of objects that reflect and transmit the illuminant. Measuring spectral properties of daylights and natural objects has been fundamental to vision research. The self-rotation of the Earth creates a 24-hour cycle within a day which periodically alters color and intensity of daylights reaching the earth’s surface. Atmospheric conditions such as cloud cover, air pollution, haze or fog modify the spectral composition of daylight [1]. The tilt of the Earth’s self-rotation axis creates a variation in the length of the daylight period across seasons and geographical locations, suggesting that understanding daylight spectra requires comprehensive measurements in spectral, temporal, and spatial domains across diverse cities and countries
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