Exposure to brighter light after waking is associated with better sleep efficiency among veterans with insomnia and a history of traumatic brain injury.

INTRODUCTION: Insomnia risk is elevated after traumatic brain injury (TBI) and can impair daily functioning. This study sought to evaluate how average and day-to-day changes in naturalistic light exposure were associated with sleep efficiency during post-TBI insomnia. METHODS: This was a secondary analysis of observational data from 28 veterans with insomnia and past TBI. Over a week, light was measured in the hour after each sleep episode's awakening (i.e., post-waking) and the hour preceding each sleep episode's lights off time (i.e., pre-sleep). Person-specific averages and day-to-day changes (i.e., changes from a person's average) in light were calculated for the post-waking and pre-sleep windows. Robust linear mixed modeling was used to estimate the associations between light variables and actigraphy-measured sleep efficiency. RESULTS: Average post-waking light exposure was positively associated with average sleep efficiency (β = 0.44, 95% confidence interval [CI]: 0.08 - 0.89). Day-to-day changes in post-waking light-exposure were positively associated with next-night sleep efficiency (β = 0.08, 95% CI: 0.01 - 0.14). Exploratory analyses revealed that this relationship was only present for veterans with low average post-waking light, such that a change from 10- to 100-lux from one day to the next was associated with a 5% increase in sleep efficiency. Light exposure prior to attempting sleep was not associated with sleep efficiency. CONCLUSION: Exposure to brighter light after waking up was associated with better sleep efficiency among veterans with insomnia and a history of TBI. For those with limited post-waking light exposure, light-based interventions may offer rapid improvement of insomnia symptoms.