The Helmholtz-Kohlrausch effect consists of two different approaches: the variable achromatic color (VAC) and variable chromatic color (VCC) methods. In. this article the difficult conceptual difference between the methods is clarified using new explanations with their schematic figures. The concept of loci with various parameters on B/L or L/Y ratios is completely different between the two methods. The VCC method can determine perceived lightness values for achromatic and chromatic colors in the whole color space. The VAC method gives perceived lightness deviation between reference achromatic color and each of the various test chromatic colors both kept at the same Munsell Value. The VAC method can never give an), information on equi. perceived lightness to test chromatic colors. Despite the difference between the two methods, misuse of the VAC method is sometimes found for perceived lightness studies of various chromatic colors. because of its ease in observations. An example is shown for the L scale of OSA-UCS. (c) 2006 Wiley Periodicals, Inc.