The long-standing absence of standardized assessment protocols for bulk photochromic materials has hindered reliable performance comparisons across studies reported by different research groups. Here, we introduce a standardized testing protocol along with a set of nine key parameters—coloration rate constant, bleaching rate constant, half-life, photostable equilibrium constant, optical modulation range, contrast ratio, response time, cycling stability and coloration efficiency—for evaluating the performance of bulk photochromic materials. Using photochromic inorganic-organic hybrid phosphonate-lanthanide-polyoxoniobates (RA-Ln-PONb, Ln = Dy, Eu, Lu; RA = risedronic acid) as a case study, we successfully validate the rationality of this protocol and demonstrate that these parameters collectively enable a comprehensive, multi-dimensional assessment of photochromic performance. This work provides an important methodological foundation for comparative studies of different bulk photochromic materials.