Evidence for an independent luminance channel.

There is a discrepancy between several studies that have shown the human luminous-efficiency function to vary with surround color and a recent study that failed to find this dependence. Data are presented that show that this discrepancy can be explained by differences in the matching techniques. Luminous efficiency measured by direct heterochromatic brightness matching does depend on surround color, whereas luminous efficiency measured by the flicker method does not. The independence of luminous efficiency as measured by flicker is evidence for an independent luminance channel.