Abstract
Whether light exposure during the day reduces non-visual light effects later in the evening has not been studied in adolescents. We investigate whether afternoon-early evening (AEE) light interventions (130 lx, 2500 lx, 4.5 hours, compared to 6.5 lx) would increase melatonin levels during later evening light exposure (130 lx) in a counterbalanced crossover study with 22 adolescents (14-17 years, 11 female). Contrary to our hypothesis, evening melatonin levels decreased after AEE bright light exposure, while sleepiness and vigilance were unaffected, and skin temperature showed no clear changes. The AEE light had acute alerting effects and bright light exposure in the 32 hours before laboratory entry was associated with higher evening melatonin and sleepiness. These findings suggest that bright AEE light increases alertness but may delay melatonin production by interfering with circadian rhythms. The study highlights the complex effects of light timing and its implications for managing adolescents’ light exposure.
Competing Interest Statement
R.L., F.F., M.D. and C.E. do not report any conflict of interest. O.S.is listed as an inventor on the following patents: ("Display system having a circadian effect on humans", US8646939B2; "Projection system and method for projecting image content", DE102010047207B4; "Adaptive lighting system", US8994292B2; "Projection device and filter therefor", WO2006013041A1; "Method for the selective adjustment of a desired brightness and/or colour of a specific spatial area, and data processing device", WO2016092112A1). O.S. is a member of the Daylight Academy, Good Light Group and Swiss Lighting Society. O.S. has had the following commercial interests in the last two years (2022-2024) related to lighting: Investigator-initiated research grants from SBB, Skyguide, VELUX and Porsche. M.S. is named as an inventor on a patent application ("Determining metameric settings for a non-linear light source", WO2020161499A1). C.C. has had the following commercial interests in the last two years (2022-2024) related to lighting: honoraria, travel, accommodation and/or meals for invited keynote lectures, conference presentations or teaching from Toshiba Materials, Velux, Firalux, Lighting Europe, Electrosuisse, Novartis, Roche, Elite, Servier, and WIR Bank
