A conventional copper sensitized photochromic glass was subjected to three excitation intensities, 21 mW/cm2, 45 mW/cm2, and 108 mW/cm2, between 0.3 μm and 0.4 μm. The effect of glass heat treatment as well as excitation intensity on the equilibrium absorption and the darkening rates is described. Results indicated that both the equilibrium absorption and the rate of darkening increase with excitation intensit