Spectral calculation is required in the design of high-quality lighting environments. Therefore, we showed the measurement results of the spectral directional reflection characteristics of building materials, and modeled them mathematically, which are the necessary input data for the spectral calculation. It was a heavy load to handle a huge amount of data for each wavelength obtained by spectral radiance measurement. Thus, we proposed a simplified method to estimate the spectral directional reflection characteristics of building materials by a simplified method to measure the overall directional reflection characteristics was extended to spectral measurements.