Additive primaries or peaks of color-matching functions are defined as peaks of complementary efficiency and of saturation per watt. These are near 447, 532, and 607 nm for all CIE illuminants. (CIE 1931 r, g, b functions peak at 447, 543, and 604 nm.) Subtractive or colorant primaries are defined as saturation minima and peaks of brightness or lightness per watt. Additive and subtractive primaries (e.g., red and cyan) are complementaries and opposites in saturation and lightness. In equal radiance color-space the six lines of constant mean saturation are invariant hues (473, 508, 574 nm and 558 c) and their complementaries.