Figure 1.

The modern light environment is complex, consisting of spectral data from a unique combination of illuminant spectra and reflected surfaces over space.

In this office setting (a), there is both direct and indirect (reflected) light. There are three direct sources: the sky (daylight), the computer screen, and the overhead fluorescent lighting. All other observed spectra are generated by source spectra interacting with objects in the scene, whose reflectance properties are not ideally diffuse (Lambertian). To simulate different representative spectral contributions in the scene (b and c), we assumed reflectance values from the IES TM-30-15 Advanced Calculation Tool [5] and a dataset of 401 illuminant spectra [6]. The resulting spectrum over the pixel area comprises a weighted average of the incident spectra. As the pixel area approaches 1, each pixel corresponds to a unique spectrum in the scene.