Anomaloscopic settings with added chromatic fields: the use of red light to reproduce protan function.

Rayleigh equations and brightness matches of spectral yellow to mixtures of spectral red and green were determined for four normal trichromats and one protanomalous trichromat. A Nagel anomaloscope, modified to allow the superposition of a chromatic field on the bipartite Nagel field, was used. The effect of adding a 650 nm. field to the Nagel field was to widen the match range toward the red end for all observers. When matching the brightness of spectral yellow to mixtures of spectral red and green, with the added 650 nm. field present, the observer required very low luminances of yellow to match reddish mixtures, behavior similar to that of protan observers. Similar results were obtained with a 620 nm. added field, but not with 2,700 K white, 490 nm., 550 nm., or 590 nm. added fields.