What does the Planckian locus represent on a chromaticity diagram?

The Planckian locus on a chromaticity diagram represents the path of colors produced by blackbody radiation as a function of temperature. A blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. When heated, a blackbody emits radiation that has a specific spectrum dependent on its temperature, which is well-described by Planck's law.

As the temperature of the blackbody increases, the color of the emitted light shifts from red at lower temperatures, through yellow, to white, and finally to blue at higher temperatures. The Planckian locus quantifies this relationship between color and temperature, allowing us to map the color appearance of light emitted by sources at various temperatures.

In the context of color science, understanding the Planckian locus is essential when discussing the color of light sources and how they relate to human color perception and the science of color matching. This understanding helps in fields such as lighting design, photography, and display technology, where accurate color representation is crucial.