Ninety-Five Percent of Six Percent: A Spectral Test of the Claim That Blue-Blocking Lenses Remove the Burden of Screen Light

Lenses marketed as blocking 95 percent of blue light are sold with the implication that they remove most of the light burden from screens. The implication does not survive band arithmetic. Under stated photopic weights for a daylight-like spectrum, the 400-450 nm band that such lenses target carries only 6.0 percent of the light the visual system actually uses; removing 95 percent of it reduces total photopic light by just 5.7 percent - the equivalent of a barely perceptible neutral dimming, leaving 94.3 percent of the light, and of any brightness-driven strain mechanism, untouched. The same lens removes 17.1 percent of the melanopic, circadian-weighted signal, a real but modest effect that belongs to sleep advice, not eye-strain claims. The claim as sold - substantial protection from screen light - is disproved by the spectrum itself; what remains true is a small circadian effect and a slight overall tint. This study is simulated, not measured.