Participants in DWL classrooms will receive conventional light from the same kind of equipment as used for the intervention group, only not applying high circadian stimulation(300lx). In order to replicate conventional lighting in the classrooms, the programming of the new LED lighting system in the control group (DWL) will meet the minimum requirements according to EN12464-181, or at least 300 lx measured at table height for a light source rated at 3000 K (warm white light).

The Munich Chronotype Questionnaire (MCTQ) is a self-reported measure of chronotype that addresses questions related to sleep and wakefulness. The participants were asked to answer the list based on experience of a typical week in their current situation.

PROMIS® (Patient-Reported Outcomes Measurement Information System) cognitive function and cognitive abilities 8a consist of 8 self-report item rated on a five point Likert scale ranging from "never" to "very often" on the Cognitive Function scale and "not at all" to "very much" on the Cognitive Abilities scale. Both PROMIS item banks show good psychometric properties, such as a high internal consistency (α =.94 for each).

The Depression, Anxiety and Stress Scale - 21 Items (DASS-21) is a set of three self-report scales designed to measure the emotional states of depression, anxiety and stress. The participants were asked to read the following statement and circle a number 0, 1, 2 or 3 which indicates how much the statement applied to the participant over the past week.

The Cleveland Adolescent Sleepiness Questionnaire (CASQ), a brief, self-completed instrument to measure excessive daytime sleepiness in adolescents. For each statement, the participants were asked to mark the circle under the response that best fits with how often it applies to them. Each item on the list is rated on a 5-point Likert scale ranging from "never" to "almost daily".

Adolescents Daytime Naps measure how often participants fall asleep daily. If they rest or fall asleep during the day, it is called a day-nap, whether they have planned to go to bed or not. Daytime hours also cover shorter periods of time when they rest or fall asleep, for example over a computer / television or reading. First participants are asked about daytime hours on weekdays and then about daytime hours on weekends. If participants go to bed more than once a day, they should record the total time staying in bed.

The participants were asked how long time they spend on a computer, tablet, game console, television, phone or other display device in the following: school lessons, work/internship, computers or social media. The answer possibilities are 0-23 hours and 0-50 minutes.

The participants were asked two questions about their physical activity during the last seven days. The participants were asked how long time per one day they usually spend participating in physical activity. Include the time they spent waking, jogging, running, cycling, exercising or doing some kind of sport. The answer possibilities range from "less than 1/2 hour a day" up to "more than 6 hours a day" The participants were also asked how many days of the last seven days they participated in physical activity for at least 60 minutes so that their heart rate increased and they sometimes got out of breath. The participation may include physical activity, workout, brisk walking, cycling in free time or transportation between different locations. The answers range from "almost never" up to "seven days".

The participants were asked how long time they usually spend sitting the last seven days. The period starts when they wake up in the morning and ends when they goes to bed for the night. Include time spent at work, at school, at home, and in their free time. This can include time spent at a desk, dining table, visiting, watching movies, reading, or in front of a television, computer, or other monitor. The answer possibilities range from "30 minutes per day" up to "more than 16 hours per day".