Physiologically relevant real-world light exposure and its behavioural and environmental determinants in Izmir, Türkiye
Abstract
Light plays a significant role in human physiology and behaviour, influencing sleep, mood, alertness and overall health. Yet light exposure remains a neglected determinant of health, with most evidence coming from high-income countries. This dataset provides the first high-resolution account of daily light exposure in Izmir, Türkiye, and is part of a series of independent collections following a common data collection protocol. The dataset includes personal light exposure measured using wearable melanopic light loggers, alongside daily questionnaires assessing sleep, mood, and physical activity, as well as structured assessments of chronotype, sleep environment, and light-related behaviours. Seventeen participants (n = 11 female, mean ± SD age 24.7 ± 2.9 years) wore three ActLumus light-logging devices continuously for seven days at the near-corneal plane, chest and wrist between December 2024 and June 2025. Compared with other participating sites, the Izmir cohort exhibited consistently delayed light exposure and sleep timing profiles, alongside reduced daytime melanopic light exposure durations. The median cumulative light exposure dose was 4.23 klx·h (Q1–Q3: 1.52–9.99) in Izmir, compared with 4.85 klx·h (1.85–11.92) in other sites (p = 0.003). The median timing of exposure above 250 melanopic lux occurred at 13:50 (12:58–14:52) in Izmir versus 13:26 (12:20–14:32) in other sites (p < 0.001). Chronotype, assessed using sleep-corrected mid-sleep on free days, occurred at 05:28 (05:07–05:56) in Izmir compared with 03:58 (03:03–04:47) in other sites (p < 0.001). Participants also reported more frequent nighttime mobile phone use, lower subjective wellbeing, and higher negative affect. Despite lower comfort and a higher proportion of negative experiences while wearing the light-logging glasses, protocol adherence remained high, with low non-wear time and generally good compliance throughout the seven-day recording period. These findings highlight how cultural, behavioural, and environmental factors may shape daily light exposure and sleep-related patterns within the Turkish context.