Delayed sleep phase syndrome (DSPS) is the most common of the circadian rhythm sleep disorders (CRSD). A person with DSPS have sufficient sleep quality, but their circadian clock is delayed compared to the normal 24-h period. They fall asleep around 03.00-04.00 at night and sleeps until 02.00-03.00 in the afternoon. This syndrome is most frequent among young people between 16-25 years, which conveys that school attendance and education are affected, and also often results in severe social consequences. DSPS is sometimes associated with depression and personality disorders and may aggravate psychiatric symptoms. This syndrome is highly underdiagnosed and there are no detailed guidelines how to treat it. The treatment usually consists of light therapy, chronotherapy or melatonin. There is a lack of guidelines how often, with which wavelength, and how long the treatment of DSPS patients shall go on. Previous studies shows that light therapy often is effective. The effect gets even better if melatonin is administered concurrently. However, the frequency of relapse is high. Thus, DSPS is a prevalent syndrome in young adults with severe consequences on normal daytime functioning. There are almost no treatment options available in health care settings. There is a clear need for further studies on this topic. The main purpose of the present study is to evaluate the clinical effects of short and long-term treatment by using light therapy and cognitive behaviour therapy (CBT). CBT is recommended at mild to moderate depression and anxiety. It also has some evidence in treating insomnia. Patients with DSPS often have al of these symptoms and therefore the investigators would like to investigate if CBT can enhance the effect of light therapy. Firstly, the investigators want to evaluate the short-term effects of light therapy with and without CBT. Secondly, the investigators want to evaluate if the patients who get CBT maintain a "normal" sleep rhythm and prevent relapse of DSPS compared to just light therapy for two weeks. The investigators also want to evaluate how this patient-group differs when it comes to behavioral factors compared to a matched reference group.
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Change from baseline in sleep-diary at 6 months.
Timeframe: Change from baseline in sleep-diary at 6 months.