This study investigated whether wearing blue-light filtering eyewear before bedtime improves cognitive alertness and sleep quality among office workers over an extended period. Given that artificial light exposure—particularly blue wavelength light from digital screens—may disrupt circadian rhythms by affecting the suprachiasmatic nucleus (SCN), researchers sought to track the long-term effects of different levels of blue-light filtration on next-day cognitive performance. The central research question was whether sustained use of high-filtration blue-light blocking glasses would produce cumulative improvements in morning alertness compared to lower filtration levels or no filtration.

Cognitive Alertness Score was operationally defined as the participant's mean reaction time in milliseconds on the Psychomotor Vigilance Task (PVT), a standardized 10-minute computer-based test administered between 8:00-9:00 AM. During the PVT, participants monitored a screen and pressed a button as quickly as possible when a visual stimulus (a red circle) appeared at random intervals between 2-10 seconds. Faster reaction times (lower millisecond values) indicated higher cognitive alertness, while slower reaction times indicated reduced alertness. Lapses, defined as reaction times exceeding 500 milliseconds, were also recorded as secondary indicators of attentional failures.²

Informed consent was obtained from all participants at baseline and reaffirmed at each subsequent assessment wave. Participants were explicitly informed of their right to withdraw from the study at any time without penalty or loss of compensation for completed sessions. The consent process included clear explanation of study procedures, potential risks (minimal), and the voluntary nature of participation. All procedures were approved by the university institutional review board prior to participant recruitment.

Over the 18-month study period, the High-Filtration group demonstrated consistent improvement in cognitive alertness, with mean reaction times decreasing from 287.3 ms at baseline to 249.8 ms at the final assessment—a reduction of 37.5 milliseconds indicating substantially faster responding and greater morning alertness. The Low-Filtration group showed more modest improvement, decreasing from 289.1 ms to 272.9 ms (16.2 ms improvement), while the Placebo Control group remained essentially unchanged across all time points (286.8 ms to 287.1 ms). This pattern indicates that higher levels of blue-light filtration correspond to progressively greater cognitive alertness scores over time, with benefits accumulating across the study duration.

The longitudinal findings support the hypothesis that sustained use of high-filtration blue-light blocking eyewear before bedtime produces cumulative improvements in next-day cognitive alertness among office workers. These results can be understood through the lens of circadian rhythms and the function of the suprachiasmatic nucleus (SCN), the brain's master biological clock located in the hypothalamus. The SCN relies on light input from specialized retinal ganglion cells that are particularly sensitive to blue wavelength light; when blue light exposure occurs in the evening, it suppresses melatonin production and delays the circadian phase, leading to reduced sleep quality and impaired morning alertness. By filtering blue light before bedtime, participants in the high-filtration condition likely experienced less circadian disruption, allowing the SCN to maintain appropriate sleep-wake timing and resulting in improved cognitive performance upon waking. However, the generalizability of these findings is limited by the sample composition: participants were exclusively corporate office workers maintaining standard 9-to-5 schedules, and results may not extend to shift workers, freelancers, individuals with irregular schedules, or those in non-office occupations.

Thornberg, M. A., Chen, W. L., & Patterson, R. D. (2023). Blue-light filtration and cognitive alertness: An 18-month longitudinal study of evening screen use in corporate employees. Journal of Sleep and Circadian Research, 41(3), 287-304. https://doi.org/10.1037/jscr0000847

1. Gender categories reflect participant self-identification at baseline. The terminology used in this study reflects current reporting standards; the researchers acknowledge that gender identity may be described differently across various cultural and temporal contexts.

2. The Psychomotor Vigilance Task (PVT) is a sustained-attention reaction time measure widely used in sleep and circadian research. A 'lapse' is operationally defined as any response exceeding 500 milliseconds, indicating a momentary failure of sustained attention often associated with sleep deprivation or circadian misalignment.