Hello.
1. Yeah, the sleep-wake cycle should be pushed backwards, rather than forwards. Due to the delayed release of melatonin, the adolescent would feel more sleepier later, and thus sleep later, and wake up later. This means that the sleep-wake cycle is delayed as their falling asleep and waking up times are shifted later. Basically, with bright light therapy, you would want to expose the individual to light (from the light box) earlier in the day, such as in the early morning, so that they are more likely to feel sleepier earlier. This is because they have been awake for longer (I'm not 100% sure on this point), and so their sleep-wake cycle would be shifted forward (or advanced), making them sleep earlier.
Hello!
I'd like to add on to what Evolio has written about the shifting of the circadian rhythm upon correction by the use of bright light therapy. Since people with an advanced sleep phase disorder are more likely to fall asleep later and wake up later due to the delayed release of melatonin, the presentation of bright light therapy early in the morning helps to 'shift the phase forward' because a rhythm cannot be reversed. If you imagine the circadian rhythm as a day (essentially the sleep-wake cycle), you will know that it goes for about 24 hours. So essentially, their 'day' is moved ahead so the person will fall asleep earlier.
People experiencing delayed sleep phase disorders are more likely to fall asleep earlier and wake up earlier. Now, this may seem contradictory to what I have written above but the use of bright light therapy at night aims to move backwards their circadian rhythm to extend the time they will fall asleep. Their rhythm is 'shifted backwards' so the time they will fall asleep is later, which is making it go 'backwards', rather than moving it ahead, like for those who are falling asleep later and waking up later.
I try to picture it like a clock and you want to wind ahead the time for those who sleep earlier and wake earlier so their day will start later as opposed to starting earlier (slowing the day and moving it backwards). For those who sleep later and wake up later, you wind back the hands of the clock face so when they wake up early, their day will start earlier instead of later (advancing the day). Regardless, you still start at one point and move from there so that's why you can't really go 'backwards' during a day when correcting for an advanced sleep phase disorder.
Please let me know if my explanation doesn't make sense! This is my logic as to approaching the contradictory nature of bright light therapy when used to shift the phase forwards or backwards.
-Mary