Due to the key role that illumination plays in determining the light reflected from objects to the eye, a complementary approach to studying constancy focuses on illumination perception. Illumination perception has been studied both directly, using tasks in which observers make explicit judgments about the illumination, and indirectly, in paradigms where inferences about the perceptual representation are made on the basis of measurements of other stimulus attributes. Studies involving direct judgments have probed the ability to perceive spatial characteristics of the illumination, including direction (Pont, van Doorn, & Koenderink,
2017; Xia, Pont, & Heynderickx,
2016), diffuseness (Morgenstern, Geisler, & Murray,
2014), and perceived distribution of illumination in space (“the visual light field”, Kartashova, Sekulovski, de Ridder, te Pas, & Pont,
2016; Koenderink, Pont, van Doorn, Kappers, & Todd,
2007; Xia, Pont, & Heynderickx,
2014; see also Schirillo,
2013). In other studies using direct assessments, observers were asked to make explicit asymmetric matches of illumination levels or directions (Khang, Koenderink, & Kappers,
2006; Rutherford & Brainard,
2002; see also Logvinenko & Menshikova,
1994). Studies using indirect judgments mainly focus on developing models of inferred illumination based on measurements of object surface reflectance (Bloj et al.,
2004; Boyaci, Doerschner, & Maloney,
2004; Fleming, Dror, & Adelson,
2003; Logvinenko & Maloney,
2006; see Brainard & Maloney,
2011) or object shape (Morgenstern, Murray, & Harris,
2011; van Doorn, Koenderink, Todd, & Wagemans,
2012). Within both approaches, efforts have been made to investigate which image cues support perceptual representations of illumination (Boyaci, Doerschner, & Maloney,
2006; te Pas, Pont, Dalmaijer, & Hooge,
2017). The study of illumination perception is often motivated by its links to object color constancy. However, the topic is also of interest in its own right, as illumination provides important information about environmental conditions, such as time of day or future weather.