Effects of Afternoon and Evening Light on Teenagers' Melatonin Levels, Alertness, Sleepiness and Sleep
Condition: Healthy; Teenager; Healthy Lifestyle
Study type: Interventional

Summary: 
      Many teenagers are familiar with this: on school days, they have to get up early; during the
      day, they hardly get any light exposure; in the evening, they go to bed late - and are then
      tired at school the next day! Around the world, teenagers are sleep deprived, with studies
      suggesting that almost half (~45%) suffer from inadequate sleep. Previous investigations have
      shown that people's sleep-wake rhythm is related to the light conditions that they are
      exposed to during the day and at night. However, little is known about how different light
      levels in the afternoon can modulate teenagers' sleep and their bodily responses to light in
      the late evening. Therefore, the investigators aim to study which lighting conditions have a
      favourable effect on these aspects and how the potentially harmful effects of light at night
      can be prevented.
    

Detailed description: 
      Light exposure during adolescence seems to be the critical component of a vicious circle. Due
      to the maturation of sleep-wake regulatory systems in combination with progressively
      ill-timed exposure to light and early school start times, teenagers suffer from the
      accumulation of sleep depth during school days. Therefore, the proposed study investigates
      whether the physiological and alerting effects of late evening light exposure in adolescents
      depend on the intensity of light exposure in the preceding afternoon (primary endpoint:
      evening melatonin concentration).

      The investigators aim to describe dose-response relationships, where the "dose" is the
      preceding (real-world applicable) afternoon light intensity (< 10 lx, ~100 lx, or >1000 lx
      EDI, three-hour duration), and the "responses" are the adolescents' physiological and
      alerting responses to evening light exposure (~100 lx melanopic EDI, 4.5-hour duration). By
      this route, the researchers can explore whether increasing afternoon light exposure is a
      feasible target for ameliorating the detrimental effects of artificial light at night and
      promoting healthier sleep-wake regulation during adolescence.
    

Intervention name(s): Low light condition; Moderate light condition; High light condition
Intervention type(s): Other; Other; Other
Intervention description(s): During the "Dim" light condition, the three-hour afternoon light exposure at the participants' eye level will be dim (<5 lx melanopic EDI). In the 4.5-hour evening light exposure, this will constitute a light intensity of ~100 lx melanopic EDI at the participants' eye level.; During the "Moderate" light condition, the three-hour afternoon light exposure at the participants' eye level will be dim (~100 lx melanopic EDI). In the 4.5-hour evening light exposure, this will constitute a light intensity of ~100 lx melanopic EDI at the participants' eye level.; During the "High" light condition, the three-hour afternoon light exposure at the participants' eye level will be dim (>1000 lx melanopic EDI). In the 4.5-hour evening light exposure, this will constitute a light intensity of ~100 lx melanopic EDI at the participants' eye level.
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: The protocol is a full within-subject trial (cross-over). All participants will conduct three 18-hour experiment sessions and go through the same protocol except for the sequence of the experiment sessions (counter-balanced and randomised).
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: melatonin; polysomnography; EEG; sleep; afternoon light; pupil size; evening light