Charts

SPD

The SPD (spectral power distribution) chart shows a representation of the radiant power emitted by a light source as a function of wavelength. The plotted SPDs incorporate linear interpolation between the wavelengths used to define the SPD. The vertical axis values are scaled to have a peak value of 1.0 at the wavelength where the spectral power is greatest; thus relative, not absolute spectral irradiance values are shown. If a combination of sources is selected with nonzero illuminance values, the SPD for each component source as well as the combined source SPD are plotted. The combined source SPD also has a peak value of 1.0 for the wavelength where the spectral power is greatest. The component source SPDs are scaled relative to their contribution to the combined source SPD. Also shown in this chart is one of two relative spectral contributions of the circadian response spectral sensitivity functions, either “warm” or “cool” as defined by Rea et al. (2021a) and Rea et al. (2021b).

Chromaticity

The chromaticity chart shows a portion of the CIE 1931 (x,y) chromaticity diagram and the calculated (x,y) chromaticity coordinates for the SPD (or the combined source SPD) as defined in CIE 15: Colorimetry, 4th edition, and represented by a filled circle. Also shown in this chart are a curved line representing the blackbody locus (the chromaticity coordinates of a Planckian radiator heated to various temperatures), and line segments representing contours of equal correlated color temperature (CCT). The terms blackbody locus, Planckian radiator, and CCT are also defined in CIE Publication 15.

Color Rendering

The color rendering chart shows a filled circle representing the SPD (or combined source SPD) in terms of its color rendering index (CRI) along the horizontal (x) axis and its gamut area index (GAI) along the vertical (y) axis. The CRI is defined in CIE 15: Colorimetry, 4th edition, and the GAI is defined in ASSIST Recommends: Recommendations for Specifying Color Properties of Light Sources for Retail Merchandising. Also shown in this chart is a rectangular region that includes CRI and GAI values between 80 and 100, inclusively. Light that falls within this region would be likely to make the color appearance of illuminated objects look colorful and natural, that is, provide good color rendering.