Spectral unmixing of light-emitting diode and high-intensity discharge illumination sources

In the recent decades, high-intensity discharge lamps, installed for public illumination, are gradually being replaced with solid-state lighting (white light-emitting diodes). This is resulting in markedly better energy efficiency, but is also raising environmental concerns related to the extra blue light emitted. Using a CubeSat, we plan to track the global progress of solid-state lighting and its contribution to light pollution. Inasmuch as the light emitted from the Earth is a mixture of a wide variety of light sources, estimating the contribution of any individual source is a challenging task referred to as spectral unmixing. In this work, we present a method for spectral unmixing of light mixtures created by a multiplicity of conventional sources, including high-intensity discharge lamps and light-emitting diodes, as measured by a spectrophotometer. We demonstrate unmixing of light into two constituent spectra, one of which is the solid-state lighting spectra, using a non-negative constrained leastsquares method with final accuracy of 93%. We furthermore show that the proposed method can be used when the mixture is captured using less than ten filtered detectors rather than a several-thousand-channel spectrometer, which is the most likely implementation on our satellite. All of our experiments have been done in a laboratory.