The phrase "solar spectrum" refers to the different colors of light produced by the sun. It includes all the colors of the rainbow, from red to violet. Full definition
Carbon nanotubes — extremely efficient absorbers of sunlight, which convert nearly the entire solar spectrum into heat — take care of that step. (scientificamerican.com)
The latter has been demonstrated to accurately reproduce the observed solar spectra during the last two minima (Shapiro et al. 2010). (aanda.org)
Ratios of synthetic solar spectra of models A (blue) and E (red) to model C. (aanda.org)