We present experimental spectra of single sonoluminescing bubble in water at different dissolved argon concentrations and excitation levels. All the relevant experimental conditions are either measured directly or derived from measured quantities for each spectrum, thus the parametric dependence of the spectra can be analyzed. To characterize the data in a given wavelength interval we fitted the shape of the spectra with the Planck function. The effective temperatures obtained from these fits lie in the range 12,000-18,000 K, practically independent of the expansion ratio, while the intensity normalized by the volume of the bubble increases with the expansion ratio as a power law. The effective temperatures decrease with the pressure amplitude for each argon concentration, while the light intensity, measured with a photomultiplier tube, increases. These observations suggest that the increased energy input due to the higher pressure amplitudes results in an increased number of less energetic photons as compared to the case of a lower excitation level.