This paper investigates the light emission efficiency of Lu2SiO5:Ce (LSO) powder scintillator under conditions employed in projection X-ray imaging. Although single-crystal LSO has been thoroughly studied in medical imaging energies, the efficiency of powder LSO has not been previously investigated experimentally under X-ray medical radiography conditions. For this purpose, three scintillating screens with a coating thickness of 63.4, 108.4, and 172.5 mg/cm2 were prepared by sedimentation of LSO powder. Measurements of luminescence efficiency (emitted light energy flux over incident X-ray energy flux) were performed in the radiographic X-ray tube voltages range (40-140 kVp). Parameters related to X-ray detection, i.e., quantum detection efficiency, energy absorption efficiency and probability of K-fluorescence reabsorption were calculated. A theoretical model, describing radiation and light transfer, was employed to fit luminescence experimental data and to estimate values of the intrinsic conversion efficiency and of the light attenuation coefficients of the scintillating screens. The spectral compatibility of the LSO powder scintillator to various optical detectors used in digital radiography was also determined by performing light emission spectrum measurements and by taking into account the spectral sensitivity of electronic optical detectors. Maximum values of LSO luminescence efficiency were observed within the range from 40 to 60 kVp. The 172.5 mg/cm2 thick screen was found more efficient than the two thinner screens examined in our experiments. The intrinsic conversion efficiency of LSO (0.10) was found close to that of currently employed phosphors. Spectral compatibility data of LSO screens indicates that LSO may be efficiently coupled to optical detectors used in digital radiography imaging systems.