I have extreme delayed sleep phase disorder (DSPD), a circadian rhythm disorder (CRD). I fall asleep at dawn and wake up early afternoon. My dim light melatonin onset (DLMO) is at 5:30 am. A normal person’s DLMO may be at 9 pm, for example.
CRD treatment—prolonged bright light after temperature nadir, dark restriction/melatonin starting several hours before natural bedtime, darkness till temperature nadir—does not work for many patients. In addition, it requires tremendous guesswork and unforgiving compliance. Even 1 day’s lapse can set some patients back for weeks. Plus, a night owl who works a day job can't live in darkness till his/her temperature nadir.
Challenge: improve treatment so it's more successful/reliable and less onerous.