Asymmetric Brightness Effects with Dark vs Light Glare-like Stimuli

A white surface surrounded by luminance gradients which are darker in the outer ends appears brighter than an equiluminant surface surrounded by uniform gray (i.e., the glare effect). Although the glare effect has been a subject of much research, its photometrical reversal (i.e., the center is dark and the outer ends of the surrounding gradients are lighter), which we dubbed as photometrical negative glare (PNG), is still left surprisingly unexplored. In the present study, perceived luminance in the center of PNG was examined. Twenty participants compared equiluminant central areas of a PNG target and a comparative one, and rated how much the latter appeared to be brighter or darker than the former. Five luminance values were employed for the equiluminant (black and four levels of gray) and three for the background (black, dark gray, and light gray). Similar conditions were set up for the glare effect, and all stimuli were repeated ten times in random order. We expected a darkening effect with PNG stimuli compared to brightness enhancements experienced with glare stimuli. Results showed instead a substantial brightness enhancement for PNG, with the exception of the black target, which showed a tendency to appear darker than the comparative one.