Color could potentially be a lagging indicator of device efficiency because, by the time the film color has noticeably changed, the concentrations of other defects (including point defects) may already be high enough to affect device performance. The precise amount of the lag depends on the point-defect chemistry, composition, and degradation pathways of the film. For the example shown in Figure and Supplementary Figure , the lag is less than 142 hours over a total test time of 800 hours. The comparison of the average colors of the samples before and after the aging test (Figure ) indicates that also subtle color changes can be quantified by the color-calibrated photographing procedure. Generally, as long as the lag remains constant or has less variability than the change of degradation onset between the target and reference samples, the optical proxy remains useful.