IMPACT OF LIGHT THERAPY ON SLEEP AND PERFORMANCE

Average sleep duration in American adults has decreased by nearly two hours over the last century, and the CDC has declared insufficient sleep a "public health problem." Inadequate sleep is linked to seven of the leading causes of death in the United States and contributes to significant economic loss through reduced productivity and accidents. While pharmacologic aids are commonly used by those with subclinical sleep issues, these often result in dependency and side effects like daytime drowsiness. Consequently, there is a clear need for non-pharmacologic interventions that can improve sleep quality and daytime alertness.

Visible light is the primary driver for synchronizing the human biological clock to the 24-hour solar cycle. Within the visible spectrum, short-wavelength "blue" light is a potent synchronizer that enhances alertness and resets circadian rhythms. Conversely, long-wavelength "red" light mimics the natural light environment of sunset and firelight; it minimally suppresses melatonin, making it less disruptive to the biological night. Despite evidence supporting light therapy for diagnosed sleep disorders, its effectiveness in individuals with subclinical sleep issues-a much larger portion of the population-remains largely unknown.

The overall objective of this study is to examine whether a combination of morning blue light and evening red light exposure can serve as an effective countermeasure for poor sleep quality and daytime fatigue. The central hypothesis is that this dual-light intervention will improve both objective and subjective sleep quality and increase subjective alertness upon awakening in adults with subclinical sleep complaints.

To test this hypothesis, the investigators will conduct a within-subject consecutive design study in 25 adults (aged 18+). Participants will first complete a 7-day baseline period to establish their habitual sleep patterns (Control condition). This is followed immediately by a 7-day intervention period (Treatment condition) consisting of 2 hours of morning blue light exposure and 2 hours of evening red light exposure. Sleep will be monitored objectively via 24-hour wrist-worn actigraphy and subjectively via daily sleep logs and the Leeds Sleep Evaluation Questionnaire (LSEQ). Subjective alertness and sleepiness will be assessed daily using the Karolinska Sleepiness Scale (KSS) and Visual Analog Scales (VAS).

Completion of this study will help bridge the gap in literature regarding light therapy's efficacy for subclinical populations. By identifying a non-pharmacological tool to improve sleep onset and morning alertness, this research aims to provide practical applications for lighting design and public health strategies to combat the risks of insufficient sleep.