Visual Light Zones

Abstract

In this article, we studied perception of a particular case of light fields that is characterized by a difference in its consistent structure between parts of a scene. In architectural lighting design, such a consistent structure in a part of a light field is called a light zone. First, we explored whether human observers are sensitive to light zones, that is, zones determined primarily by light flow differences, for a natural-looking scene. We found that observers were able to distinguish the light conditions between the zones. The results suggested an effect of light zones’ orientation. Therefore, in Experiment 2, we systematically examined how the orientation of light zones (left-right or front-back) with respect to a viewer influences light inferences in symmetric scenes. We found that observers are quite sensitive to the difference in the light flow of the light zones. In addition, we found that participants showed idiosyncratic behavior, especially for front-back-oriented light zones. Our findings show that observers are sensitive to differences in light field structure between two parts of a scene, which we call visual light zones.

Quantifying spatial, temporal, angular and spectral structure of effective daylight in perceptually meaningful ways

“…The scenes included a variety of colored surfaces in both rural and urban settings. They were chosen to contain surfaces that were partly lit by sunlight and partly in the shade as to capture two light zones [42,43] in the light field. In each of the 24 scenes, the local light fields of the sample points in the light and shade were acquired within 1 minute, yielding a total of 48 local light field measurements.…”

Visual perception and natural illumination

“…Observers can adjust the intensity, direction and diffuseness of illumination on spherical probes at different locations with reasonable accuracy within a simple photographed scene (Koenderink et al, 2007) or in real scenes (Xia, Pont, & Heynderickx, 2014, 2017c. Light field estimates are somewhat simplified compared to ground truth structure, and biased toward diverging light fields (i.e., light radiating from a source; Kartashova, Sekulovski, de Ridder, te Pas, & Pont, 2016) but do represent different 'light zones' (Kartashova, de Ridder, te Pas, & Pont, 2018). Gilchrist (1977) demonstrated that observers' reflectance judgements can change dramatically depending on the perceived location, and therefore the perceived local illumination of a surface patch.…”

Estimating lighting direction in scenes with multiple objects

“…Although our perception of illumination has received insufficient psychophysical examination (Gilchrist, 2006 ; Schirillo, 2013 ), there is evidence that the visual system infers the lighting conditions in a scene. Observers can estimate the properties of a light source based on an object’s appearance (Kartashova, Sekulovski, de Ridder, te Pas, & Pont, 2016 ; Kartashova, de Ridder, te Pas, & Pont, 2018 ; Koenderink, Pont, van Doorn, Kappers, & Todd, 2007 ) and these estimates are evident in observers’ perception of surface reflectance (Boyaci, Maloney, & Hersh, 2003 ; Boyaci, Doerschner, & Maloney, 2004 ). Furthermore, the lighting conditions at different spatial locations in a scene can be accounted for when judging surface reflectance (Gilchrist, 1977 , 1980 ; Mizokami, Ikeda, & Shinoda, 1998 ), with the observers relying on information given by multiple lighting cues (e.g., specular and non-specular objects) within a scene to make their judgements (Boyaci, Doerschner, & Maloney, 2006 ; Snyder, Doerschner, & Maloney, 2005 ).…”