Spectral power distribution

Optical properties such as transmittance, reflectivity, and absorbance as well as the sensor response are typically dependent on the incident wavelength.

The spectral power distribution over the visible spectrum from a source can have varying concentrations of relative SPDs.

The interactions between light and matter affect the absorption and reflectance properties of materials and subsequently produces a color that varies with source illumination.

This stems from the optical phenomenon called Rayleigh scattering which produces a concentration of shorter wavelengths and hence the blue color appearance.

While the human visual response integrates over all wavelengths, the relative spectral power distribution will provide color appearance modeling information as the concentration of wavelength band(s) will become the primary contributors to the perceived color.

CIE standard illuminant spectral power distribution comparisons referenced to the human visual system photopic response
Characteristic spectral power distributions (SPDs) for an incandescent lamp (left) and a fluorescent lamp (right). The horizontal axes are in nanometers and the vertical axes show relative intensity in arbitrary units.
Figure showing the greater proportion of blue light scattered by the atmosphere relative to red light.
Color temperature comparison of common electric lamps
Color temperature comparison of common electric lamps