surface in tristimulus space that represents the locus of colour stimuli of zero luminance
Note 1 to entry: The alychne passes through the origin of the space. It intersects any chromaticity diagram in a straight line which is also called the alychne; this line lies wholly outside the domain of chromaticities bounded by the spectrum locus and the purple boundary.
Note 2 to entry: This entry was numbered 845-03-43 in IEC 60050-845:1987.
Note 3 to entry: This entry was numbered 17-36 in CIE S 017:2011.