Without sunlight, imaging devices typically depend on various artificial light sources. However, scenes captured with the artificial light sources often violate the assumptions employed in color constancy algorithms. These violations of the scenes, such as non-uniformity or multiple light sources, could disturb the computer vision algorithms. In this paper, complex illumination of multiple artificial light sources is decomposed into each illumination by considering the sensor responses and the spectrum of the artificial light sources, and the fundamental color constancy algorithms (e.g., gray-world, gray-edge, etc.) are improved by employing the estimated illumination energy. The proposed method effectively improves the conventional methods, and the results of the proposed algorithms are demonstrated using the images captured under laboratory settings for measuring the accuracy of the color representation.