Personal light treatment devices: a countermeasure to improve sleep, fatigue, and circadian misalignment in an operational setting.

Carefully timed light exposure is a promising countermeasure to overcome the negative sleep and circadian implications of shift work. However, many lighting interventions are static and applied at the group level (e.g. light banks, changes to ambient lighting), which is not appropriate for all populations or settings. This study investigates whether individualized lighting exposure, via personal light treatment devices (PLTDs), can improve sleep, sustain projected performance, and entrain circadian rhythms with the work schedules of US Navy submariners. Submarines are a unique testbed for PLTD intervention because they provide a self-contained environment with little influence from outside schedules or lighting. Forty-two submariners were pseudo-randomly assigned to either the PLTD or Control group. PLTD group participants wore blue-light exposure glasses for ~40 minutes upon waking and blue-blocking glasses for ~2 hours before sleep; Control group participants did not use PLTDs. Both groups completed questionnaires assessing subjective sleep and mood before and after the 12-day intervention, and wore wrist actigraphy devices to objectively assess sleep, projected performance, and predicted circadian phase outcomes. Compared with the Control group, several objective and subjective sleep outcomes and projected performance scores were improved in the PLTD group. The PLTD group's predicted circadian phase (modeled from actigraphy-derived accelerometer data) more rapidly shifted to align with scheduled work periods. Compliance with PLTD use was high, with no major disruptions to operational duties reported. These data provide initial support for the use of PLTDs as a flexible and customizable countermeasure for fatigue, sleep loss, and circadian misalignment in an operational environment.