This research had two goals. First, a new method of very-long-term chromatic adaptation was compared to an older method of long-wavelength ambient illumination. In the new method, the observer viewed for 1 h per day for 12 or 14 days a CRT screen composed of oriented lines that appeared red. One observer also replicated a previous procedure (Neitz et al., 2002) in which she was exposed to long-wavelength room illumination for 4 h per day for 14 days. For both methods, equilibrium yellow was measured each day about 20 h after the end of the adaptation period. Both methods of very-long-term chromatic adaptation gave similar results. Second, shifts in equilibrium yellow were measured over a 30:1 range of light levels to determine if changes in color percepts were explained solely by a gain change in cone sensitivities (von Kries coefficient law). The magnitude of shift of equilibrium yellow depended on the level of the test light, which was not consistent with a gain theory of very-long-term chromatic adaptation.
