A method is proposed to construct metameric pairs for illuminant detection. The proposed method allows the quick and effective determination of the illuminant type. According to this method, a metameric black spectrum set is initially decomposed from the Standard Object Colour Spectra Database under the target illuminant based on the matrix R theory. Subsequently, a metameric sample set of the target sample is obtained by adding a metameric black to any target sample. After eliminating the samples that exhibit negative spectra, the sample with the largest metamerism index is selected to construct a metameric pair, with the general metamerism index as an evaluation index. Further, the proposed method is used to construct metameric pairs under four standard illuminants. The validity of the proposed method can be verified by calculating the color-difference value of the metameric pairs under different illuminants. The experimental results demonstrate that the metameric pairs exhibit a significant color-difference level under non-target illuminants and they can effectively determine the target illuminant type.