Optimizing the Potential Utility of Blue-Blocking Glasses for Sleep and Circadian Health.

Purpose: Wearable filters that reduce light in the short wavelength region of the visible spectrum, or "blue-blocking glasses," are increasingly available and offer an individualized, low-cost tool for enhancing sleep and circadian health. However, their effectiveness depends on filtering properties, application, timing, and implementation. If these factors are disregarded, blue-blocking glasses may be ineffective or lead to counterproductive outcomes. Methods: We introduce a new metric, melanopic daylight filtering density (mDFD), to quantify a filter's capacity to decrease melanopic input, providing an alternative to ad-hoc measures. We applied mDFD to 26 commercially available glasses, estimating their potential to reduce circadian and related physiological effects of light across common applications in the context of consensus-based metrics and recommendations. We also reviewed intervention studies that used blue-blocking glasses. Results: Products varied considerably in mDFD, with only those rated at mDFD ≥1 providing sufficient reductions in melanopic input to justify the "blue-blocking" label and associated claims. At least one relevant sleep or circadian-related outcome improved with blue-blocking interventions in the studies reviewed. In addition to filtering strength, appropriate timing and usage are critical to effectiveness. Conclusions: The efficacy of blue-blocking glasses depends on both spectral filtering and proper usage. The mDFD metric offers a consistent, evidence-based approach for evaluating, selecting, and designing products that reduce photic input for non-visual physiological effects of light. Translational Relevance: Standardized characterization of blue-blocking glasses using mDFD facilitates reliable product comparisons, evidence-based selection, and rational design of lenses that are optimized for circadian health across a range of applications.