Electronic display devices used before bed may negatively affect sleep quality through the effects of short-wavelength (blue) light on melatonin production and the circadian cycle. We quantified the efficacy of night-mode functions and blue-light–reducing lenses in ameliorating this problem.
The purpose of this study was to compare the radiation produced by smartphones that reaches the eye when using night-mode functions or blue-light–reducing spectacle lenses.
Radiant flux of 64 smartphones was measured with an integrating sphere. The retinal illuminance was calculated from the radiant flux of the smartphones. For the night-mode functions, the spectra produced by the smartphones were measured. The transmittance of four blue-light–reducing spectacle lenses, which filter light with either antireflective coatings or tints, was measured using a spectrometer. To determine the impact of blue-light–reducing spectacles, the radiant flux of the smartphone was weighted by the transmission spectrum of these glasses. Visual and nonvisual (circadian) parameters were calculated to compute the melatonin suppression values (MSVs) through a logistic fitting of previously published data. The MSV was used as the figure of merit to evaluate the performance of blue-light spectacles and smartphone night-mode functions.
Night-mode functions in smartphones reduced MSVs by up to 93%. The warmest mode produced the least suppression. Blue-light–reducing spectacles reduced melatonin suppression by 33%, the coated lenses being more efficient than tinted lenses.
All smartphones in this study emit radiant power in the short-wavelength region of the visible spectrum. Such smartphones may impair the regulation of circadian cycles at nighttime. The activation of night-mode functions was more efficient than the commercially available blue-light–reducing spectacle lenses in reducing the amount of short-wavelength light (up to 2.25 times). These results can be extrapolated to most electronic devices because they share the same type of white radiant sources with smartphones.