The room was dark and the room temperature was set to 22OC. Participants sat in front of the computer screen for two hours and performed onscreen tasks between 21:00h and 23:00h. Tasks were reading texts and answering related questions, writing exercises and solving verbal and arithmetic problems. Participants were not informed of the differing light conditions and were told that the purpose of the study is to examine the effect of the content of the tasks on sleep.