Dominant Wavelength

In the x, y chromaticity diagram shown below, the curve VSCSR is the spectrum locus, and point N is the white point (the chromaticity point of the perfect reflecting diffuser). Colors located in the region enclosed by the spectrum locus and the straight lines VN and NR are referred to as spectral colors; colors located in the triangle NVR with the white point N at the apex and the pure purple line VR as the base are referred to as non- spectral colors.

Dominant wavelength (spectral colors)

For spectral colors, the dominant wavelength (generally symbolized as λd) is the wavelength corresponding to the point on the spectrum locus (the curve VSCSR) where a line drawn from the white point through the chromaticity point obtained from the measured values intersects the spectrum locus. In the example shown, for a measured chromaticity point C, the dominant wavelength is the wavelength corresponding to point S, where the extension of line NC from the white point N through chromaticity point C intersects the spectrum locus.

Complementary wavelength (non-spectral colors)

For non-spectral colors, a line drawn from the white point through the chromaticity point obtained from the measured values does not intersect the spectrum locus (the curve VSCSR), and instead intersects the pure purple line, which has no corresponding wave- lengths. In such case, the complementary wavelength (generally symbolized as λc) is used instead of the dominant wavelength. The complementary wavelength is determined by extending the line in the opposite direction, from the chromaticity point through the white point to the spectrum locus, and using the wavelength corresponding to the point of intersection. In the example, chromaticity point C’ is in the non-spectral region; the complementary wavelength is the wavelength corresponding to point SC, where the line extended from C’ through white point N intersects the spectrum locus.

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