The possibility of using lasers diodes and a fiber optic trifurcated for the evaluation of the power optic absorbed on coals samples is studied. The method is based on scanning of samples using lasers diodes with the wavelengths 632,8nm, 532nm, 405nm, and calibration plots of the reflected luminosity of the selection as function of the absorbance of coals. In this paper we showed the calibration plots and the colorimetric parameters of coals calculated from the absorption or diffuse-reflectance. The advantages of the method are its high performance for estimating the colorimetric parameters of coals samples, quality control of industrial processes and classification of coals.