Planckian locus

The curve on a chromaticity diagram traced by the colors of ideal blackbody radiators as their temperatures vary. It provides a reference for describing the chromaticity of white light.

Planck's law: A formula giving the spectral radiance of black-body radiation as a function of wavelength and temperature. It determines the spectrum converted into each chromaticity point.
Color temperature: A temperature-based description of a light source's perceived color, commonly expressed in kelvins. The locus gives color temperature a precise blackbody reference.
Spectral power distribution: The distribution of a light source's radiant power across wavelengths. Each temperature supplies a different distribution before chromaticity is calculated.
Daylight locus: The curve approximating the chromaticities of natural daylight at different correlated color temperatures. It models daylight chromaticities, which depart from the blackbody-based curve.
CIE 1931 color space: A color space defined by the CIE in 1931, including the XYZ tristimulus system and xy chromaticity diagram. The familiar locus is plotted on its xy chromaticity diagram.
Daylight (color temperature): The color of daylight described by its correlated color temperature, which varies with atmospheric and solar conditions. Daylight chromaticities are often compared with the locus despite not being blackbody radiation.
CIE 1931 color-matching functions: Three wavelength-dependent functions defining the CIE 1931 standard observer's color-matching response. They convert blackbody spectra into tristimulus values for the diagram.
Color rendering index: A measure comparing how a light source renders object colors with a reference illuminant. Matching the locus does not establish how faithfully a source renders object colors.
Chromaticity: The attribute of color determined by its hue and saturation, independent of its luminance. The locus tracks chromaticity while omitting the radiance level of each radiator.
White point: The chromaticity designated as white in a color space or imaging system. Locus positions help specify warm-to-cool white points.

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