0012 Shedding Light on Chronotype: Bedroom Lighting Behavior Predicts Circadian Preference

Abstract Introduction Artificial light can extend photoperiods beyond the natural daylength. This has been posited as a contributor to individual differences in chronotype, supported by the seminal camping study in which eliminating artificial light compressed and aligned chronotype with the natural daylength. However, this position includes an untested assumption that the unique contribution of artificial lights (i.e. above natural ambient light) is associated with chronotype. This study assessed this relationship using smart technology to capture artificial lighting use in the bedroom. Methods Participant bedrooms (n=15) with standardized smart-bulbs were monitored for two weeks. Light usage and behaviors were tracked using a wireless switch and a wall-mounted spectrometer that measured both photopic (p-lux) and melanopic lux (m-lux). Chronotype was measured using the Morningness–Eveningness Questionnaire (MEQ; range = 42 – 62, mean = 49 ± 10 SD). MEQ scores were correlated with changes in p-lux and m-lux after light-switch presses during the morning (03:00–11:00) and evening (17:00–03:00). Results In the morning, turning lights on only resulted in a small increase in ambient light (30 p-lux, 13 m-lux), and bedrooms largely remained dim despite lights on (92% 100 lux). Even still, greater changes from artificial light in the morning was significantly associated with more morningness (βp-lux=.84, βm-lux=.66). In the evening, turning lights on also increased ambient light slightly (24 p-lux, 16 m-lux), and bedrooms almost always remained dim (98% 100 lux). Evening bedroom light use and chronotype was not statistically significant (βp-lux=.57, βm-lux=.19). Notably, 78% of all bedroom light use occurred in the evening. Conclusion Results suggest that most bedrooms are dimly lit ( 100 lux) and that artificial lights contributed minimal additional brightness ( 30 lux); however, use of artificial bedroom light in the morning had a stronger association with chronotype than in the evening. One explanation may be sensitization to light in the morning due to dark-adaptation during sleep. Future research should use longitudinal or interventional approaches to allow for directional inferences. These results underscore the need for awareness of how home lighting may contribute to circadian health. Support (if any) R01HL177767