Change in hue of spectral colors by dilution with white light (Abney effect).

Monochromatic light, when mixed with white light, not only becomes desaturated but also changes in hue ( Abney effect). This effect was studied in three observers by using three unique hues (blue, green, and yellow) and four compound (intermediate) hues. The whites used for desaturation ( desaturants ) included Abney 's white (3890 K), two bluish whites (10,000 and 20,000 K), and each observer's own, perceptually neutral white (6200-6980 K). Test stimuli of 0.5 degree diameter were presented to the dark-adapted fovea for 1 sec in a dark surround. Abney 's results were confirmed, except in the shortwave and middle-wave parts of the spectrum. At short wavelengths we always observed a hue shift toward increasing redness, whereas Abney reported a shift toward blue. At middle wave-lengths (500-556 nm), we found smaller effects than did Abney . Here Abney 's white produced an increase in perceived yellow, whereas all other desaturants produced an increase in perceived green. Two colors, blue-green and yellow, changed least. In general, the hue shifts increased with decreasing colorimetric purity (from 1.0 to 0.5). The results are discussed in relation to color additivity, constant-hue loci, and the Benzold -Br ucke effect.