P028 Sleep depth and wake propensity measured with the Odds-Ratio Product (ORP) in a shift work protocol comparing two lighting interventions

Abstract ORP is a continuous metric of sleep depth and wake propensity, which distinguishes different levels of sleep depth within the same conventional sleep stage. Circadian-informed lighting may improve sleep depth compared to regular, dim lighting. Previous analyses found that circadian-informed lighting extended N2 sleep compared to standard lighting. The present study used ORP to further elucidate sleep effects under different lighting during shift work. Nineteen healthy sleepers (12 males, mean±SD 29±10yrs) underwent two 8-day sessions (circadian-informed versus standard lighting). During days 3-7, participants transitioned to night work, sleeping from 10:00–19:00. ORP was calculated using C3 and C4 electrodes in 3-sec epochs. Values ranged from 0 (very deep sleep) to 2.5 (full wakefulness). Main outcomes included average ORP and ORP post-arousals (ORP-9), with lower ORP-9 suggesting rapid return to deep sleep. Linear mixed models demonstrated a significant main effect of day on average ORP in N3 (F (4, 143.13) = 2.64, p=.037). Pairwise comparisons showed a significant increase in average ORP in N3 from day 2 to day 5 (p=.028), implying a lighter sleep in both lighting conditions as the study progressed. Two significant two-way interactions (condition*day) on average ORP-9 measured on the right hemisphere (F (4,125.35) = 3.31, p=.013) and on average ORP in wake (F (4,149.43) = 2.46, p=.048) were found; however, pairwise comparisons were not significant. Our results indicate that the increase in sleep duration with circadian-informed lighting is not associated with changes in sleep depth. Results suggest that sleep changes with circadian informed lighting are complex.