Embodiments described herein correct errors in spectrometer outputs due to the presence of second-order light. Embodiments determine a relationship between first-order light and second-order light of the spectrometer output. The relationship is a function of wavelength and an output of the spectrometer due to the first-order light. The relationship is used to determine an estimated contribution of the second-order light to the output. Spectrometer errors introduced by the second-order light are corrected by adjusting the spectrometer output according to the estimated contribution of the second-order light.