Brightness Difference and Its Relation to the Distinctness of a Border

The border between precisely juxtaposed chromatic (600 nm) and achromatic fields is as distinct when the fields are equally bright as when the chromatic field is brighter. The relative brightnesses of precisely juxtaposed chromatic and achromatic fields can be adjusted so that the border between them is minimally distinct. When the border is least distinct, the chromatic field will appear slightly brighter than the achromatic one. When the brightness of the achromatic field is increased to match that of the chromatic field, the distinctness of the border increases. When this added white light is removed from the achromatic field and added to the already brighter chromatic field, the distinctness of the border remains approximately constant. These results make questionable the usefulness of the concept of brightness contrast.