The aim of the present study was to investigate the absolute luminescence efficiency (AE) of a CaWO₄ screen, under X-ray irradiation and to compare it with a custom made PMMA/Gd₂O₂S:Tb composite film screen. The emitted light was evaluated by performing measurements of the AE under X-ray exposure conditions, with tube voltages ranging from 50 to 125 kV. The spectral compatibility of the CaWO₄ screen, with various existing optical detectors, was investigated after emission spectra measurements. AE was found maximum at 50 kVp (2.34 Efficiency Units-E.U) which was slightly lower than the corresponding “gold standard” Gd₂O₂S:Tb (2.67 E.U), at the same X-ray energy. The emission spectrum of CaWO₄ is excellent matched with the spectral sensitivities of photocathodes and silicon photomultipliers often employed in radiation detectors, and with good matching with amorphous silicon photodiodes. Considering the adequate luminescence efficiency values and the spectral compatibility with various photodetectors, CaWO₄ could be also considered for use in X-ray imaging devices such as charged-coupled devices (CCD) and complementary metal oxide semiconductors (CMOS).