The disclosure is directed to a system and method of controlling spectral attributes of illumination. According to various embodiments, a portion of illumination including an excluded selection of illumination spectra is blocked, while another portion of the illumination including a transmitted selection of illumination spectra is directed along an illumination path. In some embodiments, optical metrology is performed utilizing the spectrally controlled illumination to enhance measurement capability. For instance, the spectral attributes of illumination utilized to analyze different portions of a sample, such as different semiconductor layers, may be selected according to certain measurement characteristics associated with the analyzed portions of the sample.