Measurements of lightness: dependence on the position of a white in the field of view

We used quantitative lightness matching to measure changes in achromatic lightness as a function of the separation between a bright White (1000 mL) and a nearby 3 or a 300 mL Test Field. The experiments varied size, angular subtend and separation of the White area. All variables showed some influence on the matching lightness to the Test Field. Of particular interest are substantial changes in lightness from White areas that have 7.5 degrees separation. This paper will describe the quantitative results and their implications for models of lightness.